U.S. patent number 9,164,277 [Application Number 13/938,276] was granted by the patent office on 2015-10-20 for micromechanical device.
This patent grant is currently assigned to Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V.. The grantee listed for this patent is Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V.. Invention is credited to Holger Conrad, Thilo Sandner, Harald Schenk, Christian Schirrmann, Jan-Uwe Schmidt, Fabian Zimmer.
United States Patent |
9,164,277 |
Conrad , et al. |
October 20, 2015 |
Micromechanical device
Abstract
The force on the electrodes of an electrostatic field is used so
that lateral tensile or compressive forces result which can deform
a deformable element or can strongly deflect a deflectable
structure. For this, a micromechanical device includes, apart from
an electrode and a deformable element, an insulating spacer layer
via which the electrode is fixed to the deformable element, wherein
the insulating spacer layer is structured into several spaced-apart
segments along a lateral direction, so that by applying an electric
voltage between the electrode and the deformable element lateral
tensile or compressive forces bending the deformable element along
the lateral direction result. Thereby, the problem that normally
accompanies electrostatic drives, namely the problem of the pull-in
effect, is overcome. The deflection of the deformable element can
be much larger than the gaps of the two electrodes, i.e. the
above-mentioned electrode and the deformable element. A usage as a
sensor is also possible.
Inventors: |
Conrad; Holger (Dresden,
DE), Schenk; Harald (Dresden, DE),
Schirrmann; Christian (Dresden, DE), Sandner;
Thilo (Dresden, DE), Zimmer; Fabian (Dresden,
DE), Schmidt; Jan-Uwe (Dresden, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung
e.V. |
Munich |
N/A |
DE |
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Assignee: |
Fraunhofer-Gesellschaft zur
Foerderung der angewandten Forschung e.V. (Munich,
DE)
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Family
ID: |
44625008 |
Appl.
No.: |
13/938,276 |
Filed: |
July 10, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20130301101 A1 |
Nov 14, 2013 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/EP2011/050483 |
Jan 14, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02N
1/006 (20130101); H02N 1/08 (20130101); G02B
26/0825 (20130101); H01G 5/16 (20130101); G02B
26/0841 (20130101); H04N 1/08 (20130101) |
Current International
Class: |
G02B
26/08 (20060101); H02N 1/00 (20060101); H04N
1/08 (20060101); H01G 5/16 (20060101) |
Field of
Search: |
;359/198.1,199.1,199.3,200.7,212.1,213.1,233.1,224.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10 2008 049 647 |
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Apr 2010 |
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DE |
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1 526 399 |
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Apr 2005 |
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EP |
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10-109284 |
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Apr 1998 |
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JP |
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2005-326620 |
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Nov 2005 |
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JP |
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2007-259691 |
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Oct 2007 |
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JP |
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2008-36774 |
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Feb 2008 |
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JP |
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02/49199 |
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Jun 2002 |
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WO |
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Other References
Official Communication issued in International Patent Application
No. PCT/EP2011/050483, mailed on Oct. 28, 2011. cited by applicant
.
Official Communication issued in corresponding Japanese Patent
Application No. 2013-548757, mailed on Jul. 29, 2014. cited by
applicant.
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Primary Examiner: Cherry; Euncha
Attorney, Agent or Firm: Keating & Bennett, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of copending International
Application No. PCT/EP2011/050483, which was filed on Jan. 14,
2011, and which is incorporated herein by reference in its
entirety.
Claims
The invention claimed is:
1. A micromechanical device, comprising an electrode; a deformable
element; and an insulating spacer layer, wherein the electrode is
fixed to the deformable element via the insulating spacer layer,
and wherein the insulating spacer layer is structured into several
spaced-apart segments along a lateral direction, so that by
applying an electric voltage between the electrode and the
deformable element an area force acting in a thickness direction is
applied to the electrode and the deformable element, as a
consequence of which lateral tensile or compressive forces result
that bend the deformable element along the lateral direction
according to the bimorph principle.
2. The micromechanical device according to claim 1, wherein the
segments each comprise a longitudinal extension direction running
transversely to the lateral direction.
3. The micromechanical device according to claim 2, wherein the
segments and the gaps between the same are stripe-shaped.
4. The micromechanical device according to claim 1, wherein a
periodicity of the structuring of the insulating spacer layer is
approximately constant in the lateral direction across an area via
which the electrode and the deformable element oppose one
another.
5. The micromechanical device according to claim 1, wherein the
deformable element is a plate, a bowl, a membrane, a beam or a
bar.
6. The micromechanical device according to claim 1, wherein the
deformable element is suspended and clamped such that it remains
unbent by applying an electric voltage along a lateral direction
perpendicular to the lateral direction, or is bent also in a same
direction as along the lateral direction.
7. The micromechanical device according to claim 1, which is formed
in a substrate, wherein the electrode is fixed in a substrate
direction above or below the deformable element, so that by bending
the deformable element the same is bend out of the substrate plane,
wherein the insulating spacer layer runs parallel to the substrate
plane.
8. The micromechanical device according to claim 1, which is formed
in a substrate, wherein the electrode is laterally fixed to the
deformable element, so that by bending the deformable element the
same is bent within a substrate plane of the substrate, wherein the
insulating spacer layer runs transversely to the substrate
plane.
9. The micromechanical device according to claim 1, wherein the
electrode is a first electrode and the micromechanical device
comprises a further electrode fixed to the side of the first
electrode facing away from the deformable element via a further
insulating spacer layer, wherein the further insulating spacer
layer is structured into several spaced-apart segments along the
lateral direction.
10. The micromechanical device according to claim 9, wherein the
spacer layer is a first insulating spacer layer and the segments of
the further insulating spacer layer are positioned laterally in
gaps of the segments of the first insulating spacer layer.
11. The micromechanical device according to claim 1, wherein the
electrode is a first electrode and the micromechanical device
comprises a further electrode fixed to a side of the deformable
element facing away from the first electrode via a further
insulating spacer layer, wherein the further insulating spacer
layer is structured into several spaced-apart segments along the
lateral direction, so that by applying an electric voltage between
the first electrode and the deformable element lateral tensile or
compressive forces result that bend the deformable element along
the lateral direction in a first direction, while by applying an
electric voltage between the second electrode and the deformable
element either the same of lateral tensile or compressive forces
result that bend the deformable element along the lateral direction
also in the first direction, or the other of the lateral or
compressive forces that bend the deformable element along the
lateral direction in a direction opposing the first.
12. The micromechanical device according to claim 1, wherein a
thickness of the insulating spacer layer is between 100 nm to 5
.mu.m, each inclusively.
13. The micromechanical device according to claim 1, wherein the
deformable element is made of a conductive material, is made
locally conductive or coated with a conductive material.
14. The micromechanical device according to claim 1, wherein the
electrode is formed in a planar manner and respectively curved away
from the deformable element between the segments.
15. The micromechanical device according to claim 1, wherein the
electrode is formed in a planar manner and respectively curved
towards the deformable element between the segments.
16. The micromechanical device according to claim 1, wherein the
electrode is formed in a planar manner and respectively comprises a
V-shaped cross-section in a plane between the segments, which is
spanned by the lateral direction and a thickness direction of the
insulating spacer layer.
17. The micromechanical device according to claim 1, wherein a
surface of the deformable element facing the electrode is
respectively formed curved away from the electrode between the
segments.
18. The micromechanical device according to claim 1, wherein a
surface of the deformable element facing the electrode is
respectively formed curved towards the electrode between the
segments.
19. The micromechanical device according to claim 1, wherein the
electrode and a surface of the deformable element facing the
electrode are respectively formed between the segments such that
gaps therebetween comprise the same cross-section in a plane
spanned by the lateral direction and a thickness direction of the
insulating spacer layer.
20. The micromechanical device according to claim 1 comprising a
driver circuit for applying the voltage to the micromechanical
device, so that the micromechanical device acts as a
micromechanical actuator.
21. The micromechanical device according to claim 1, wherein the
deformable element forms a spring portion between a suspension
location and a functional element of the micromechanical
device.
22. The micromechanical device according to claim 21, wherein the
functional element comprises a plate tiltably suspended around a
tilting axis, and the spring portion forms a first distributed
spring of the micromechanical device, which extends opposite to a
second distributed spring of the micromechanical device along a
circumference of the plate from a torsion spring of the
micromechanical device, which extends along the tilting axis to a
mounting location at the circumference of the plate, namely
symmetrically to the second distributed spring.
23. The micromechanical device according to claim 22, further
comprising a further electrode fixed to the second distributed
spring via a further spacer layer, such that in the first
distributed spring the insulating spacer layer is structured such
that by applying an electric voltage between the electrode and the
deformable element lateral tensile and compressive forces result
that bend the first distributed spring relative to the plate in a
first normal direction, and wherein in the second distributed
spring the insulating spacer layer is structured such that by
applying an electric voltage between the electrode and the
deformable element lateral tensile and compressive forces result
that bend the second distributed spring relative to the plate in a
second normal direction opposing the first.
24. The micromechanical device according to claim 1, wherein the
deformable element forms a spring portion between a suspension
location and a functional element of the micromechanical device,
wherein the function element comprises a plate tiltably suspended
around a tilting axis, and the spring portion forms a first beam of
an Y-shaped spring of the micromechanical device running parallel
to the tilting axis, which extends parallel to a second beam of the
Y-shaped spring of the micromechanical device, namely symmetrical
to the tilting axis, wherein the micromechanical device further
comprises a further electrode fixed to the second beam via a
further spacer layer, such that in the first beam the insulating
spacer layer is structured such that by applying an electric
voltage between the electrode and the first beam lateral tensile or
compressive forces result that bend the first beam relative to the
plate in a first normal direction, and in the second beam the
insulating spacer layer is structured such that by applying the
electric voltage between the electrode and the second beam lateral
tensile or compressive forces result that bend the second beam
relative to the plate in a second normal direction opposing the
first.
25. The micromechanical device according to claim 1, wherein the
deformable element forms a spring portion between a suspension
location and a functional element of the micromechanical device,
wherein the functional element comprises a plate suspended at a
suspension point along its circumference, and the spring portion
forms one of four portions of a U-shaped spring of the
micromechanical device, which extends from the suspension point
along the circumference of the plate and back to the suspension
location, wherein the U-shaped spring bends when the plate is
deflected at the suspension point from a resting position plane at
the four portions arranged serially along the U-shaped spring
alternatively in one and then in the opposite direction relative to
the resting position plane, wherein the micromechanical device
further comprises further electrodes fixed to the other of the four
portions via further spacer layers, namely such that in the first
and third portion from the suspension location or the suspension
point lateral tensile or compressive forces result by applying an
electric voltage between the electrode and the respective portion
that bend the respective portion relative to the plate in a first
normal direction, and in the second and fourth portion from the
suspension location or the suspension point lateral tensile or
compressive forces result by applying an electric voltage between
the electrode and the respective portion that bend the respective
portion relative to the plate in a second normal direction opposing
the first, wherein a further U-shaped spring is formed
symmetrically to the U-shaped spring relative to a connecting line
of suspension location and suspension point.
26. The micromechanical device according to claim 22, wherein the
plate is suspended symmetrically to an axis perpendicular to the
tilting axis or connecting line.
27. The micromechanical device according to claim 21, wherein the
functional element comprises an optical element, such as a mirror,
a dispersive element or a diffractive element or an AFM measuring
tip.
28. The micromechanical device according to claim 1, wherein the
deformable element is a plate and the segments form concentric
circles, so that the lateral tensile or compressive forces
resulting by applying the electric voltage between the electrode
and the deformable element bend the plate in a helmet or a bowl
shape.
29. The micromechanical device according to claim 28, wherein the
plate is a mirror plate.
30. The micromechanical device according to claim 1, wherein the
electrode is formed in a planar manner and respectively curved
towards the deformable element between the segments; and a surface
of the deformable element facing the electrode is respectively
formed curved away from the electrode between the segments; so that
the bending of the deformable element results due to a lateral
contraction of portions of the deformable element between the
segments of the insulating spacer layer in the thickness direction
away from the deformable element.
31. The micromechanical device according to claim 1, wherein the
electrode is a first electrode and the micromechanical device
comprises a further electrode fixed to the side of the first
electrode facing away from the deformable element via a further
insulating spacer layer, wherein the further insulating spacer
layer is structured into several spaced-apart segments along the
lateral direction; and wherein the spacer layer is a first
insulating spacer layer and the segments of the further insulating
spacer layer are positioned laterally in gaps of the segments of
the first insulating spacer layer.
32. A sensor comprising a micromechanical device according to claim
1, further comprising a detector circuit for detecting the
capacitance between the electrode and the deformable element of the
micromechanical device.
33. An energy generator comprising a micromechanical device
according to claim 1, further comprising a voltage source for
applying a constant voltage between the electrode and the
deformable element, so that due to an externally induced bending of
the deformable element a current flow is generated between the
electrode and the deformable element.
34. An energy generator according to claim 33, wherein a weight or
a plate is mounted to the unfixed end of the deformable element.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a micromechanical device, such as
a micromechanical actuator or a micromechanical sensor.
Micromechanically produced and actively deflectable beam and plate
structures are used for a large number and variety of applications.
The deflectable plates are frequently also referred to as membranes
due to their low thickness. For the actively deflectable beams, the
term cantilever is frequently used. Table 1 lists some examples of
microsystems and the functional principle of the actively
deflectable microstructures is explained.
TABLE-US-00001 TABLE 1 Examples of microsystems and a description
of possible functional principles of the deflectable
microstructures Functional principle of the actively Example/
Microsystem deflectable microstructures reference Actively bendable
Thin mirror plates firmly clamped at the 0, [2], mirror for focus
edge are bent using an electrostatic field. [3], [8], variation of
light Here, the forces from the electrostatic field [9] beams or
for are effective vertically at the bottom of the specific plate.
correction Thin mirror plates are bent using an 0, [4], of the
phase of the actively adjustable lateral material strain [5], [11]
wave front of light within a material layer (bimorph or monomorph
principle). The actively amendable lateral material strain can have
a thermomechanical, piezoelectric, piezomagnetic, electrostrictive
or magnetostrictive origin. Actively bendable Thin annular mirror
plates firmly clamped [21] focusing mirror at the edge are bent
using an electrostatic array for trans- field. Here, the forces
from the missive displays electrostatic field are effective
vertically at the bottom of the plate Actively tiltable The mirror
plates are connected to a [6] mirrors for spatial stationary frame
via spring elements and [7] deviation of light are tilted using an
electrostatic field. Here, beams the forces from the electrostatic
field are effective vertically at the bottom of the plate. This
principle is also used for micro tilting mirror arrays. The mirror
plates are connected to a [10], stationary frame via thin bimorph
or [12], monomorph beam structures. Tilting the [13] mirror plate
is performed via an actively adjustable layer stress and the
associated bending of the beam structures. The active amendable
lateral material strain can have a thermomechanical, piezoelectric,
piezomagnetic, electrostrictive or magnetostrictive origin.
Actively adjustable The mirror plates are connected to a [15]
lifting or lowering stationary frame via spring elements and mirror
for the are moved orthogonally to the mirror area phase variation
of using an electrostatic field. Here, the forces light (e.g. in
FTIR from the electrostatic field are effective spectrometers)
vertically at the bottom of the plate. This principle is also used
for lowering mirror arrays for adaptive optics. The mirror plates
are connected to a [14] stationary frame via thin bimorph or
monomorph beam structures. Deflection of the mirror plate is
performed via an actively adjustable layer stress and the
associated bending of the beam structures. The actively amendable
lateral material strain can have a thermomechanical, piezoelectric,
piezomagnetic, electrostrictive or magneto-strictive origin. Atomic
Force A beam (=leaf spring or cantilever) is Microscopy deflected
either via an electrostatic field (AFM) in measure- between the
measurement probe and the tip ment modes with of the beam or via
piezoelectrically dynamic excitation induced strain within the
beam.
Basically, the functional principles of the actively deflectable
microstructures presented here can be divided into two classes:
In the first class, a force acts orthogonally to the structure 100
(=beam or plate) to be deflected.
FIG. 43 exemplarily shows a micromechanical actuator of this type.
FIG. 43 shows a micromechanical device having a deflectable plate
or a deflectable beam 100, which is cantilevered in the present
case and where an externally effected force F is effective, which
brings the plate or the beam 100 perpendicular to the extension
direction out of its resting position, as is indicated by an arrow
100a between the resting position on the left and the deflected
position on the right in FIG. 43. Here, it should be noted that in
the overall document of the present application the included
drawings and sketches include schematical coordinate symbols marked
by x, y and z, and that here it has been consistently taken care
that the x-y plane is parallel to the substrate plane or the chip
plane, in the case that the shown devices are integrated in a chip,
and that accordingly the z direction is orthogonally to the
substrate plane in the case that chip integration exists.
Frequently, the vertically attacking force F is the force from an
electrostatic field. Here, the electrostatic field E is generated
using an electric voltage U between the beam (or plate) to be
deflected and a stationary electrode 101 (also referred to as
counter-electrode).
FIG. 44 shows a micromechanical actuator wherein the structure 100
to be deflected is deflected in that a voltage U is applied between
the structure 100 to be deflected and an electrode 101 opposing the
same, which has the effect that the structure 100 to be deflected
and the electrode 101 are attracted toward each other. Thus, in the
case of FIG. 44, the structure to be deflected, here a cantilevered
beam or plate, is deflected by the force of an electrostatic
field.
The reason for the dominance of the electrostatic drive in
microsystem technology is the good scaling behavior of the forces
(acting on the electrodes of an electrostatic field) in the
dimensions common for microsystems. For simple, plane parallel
electrode assemblies performing no or only very little movement,
the force is inversely proportional to the square of the electrode
gap (F.about.1/d.sup.2). Thus, small electrode gaps result in a
high force effect on the electrodes.
The deflection w of the microstructures (beams or plates) depends
in an approximately square manner on the applied electric voltage U
(for plane parallel electrode assemblies F.about.1/d.sup.2). The
basic curve is shown in FIG. 45.
The first region of this characteristic curve is characterized by a
stable equilibrium between the forces of the electrostatic field
and the restoring forces of the clamp. The second region is
characterized by an unstable equilibrium. A small change of the
electric voltage has the effect that the forces of the
electrostatic field become larger than the mechanical restoring
forces of the clamp (=holder of the microstructure). The beam (or
the plate) 100 thus reaches an unstable area and is accelerated up
to the counter-electrode 101. This behavior is known to a person
skilled in the art as "pull-in effect": The pull-in effect occurs
in all electrostatically deflectable microstructures. The maximum
possible deflection w.sub.pull-in is limited (depending on the
mechanical characteristics of the clamp) to a maximum of approx.
1/3 of the electrode gap d by the pull-in effect. Large deflections
can only be enabled by large gaps d of the electrodes. Large gaps,
however, significantly increase the necessitated electric drive
voltages (due to: F.about.1/d.sup.2).
Due to the pull-in effect and the ratio F.about.1/d.sup.2, a large
deflection of electrostatically deflectable microstructures is
combined with high electric voltages. Voltages in the range of 100
V are frequently common for deflections in the .mu.m range (e.g.:
[2] and [3]).
In a second class of microstructures, a lateral force acts within
one or several layers of the structure 200 to be deflected.
FIG. 46 shows a structure 200 to be deflected composed of a layer
stack of two or more layers 201 and 202. A lateral strain is
generated in at least one of the layers, by the force of which the
structure 200 to be deflected, here again for example a beam or a
plate, is deflected, as is indicated by 200a.
This form of deflectable structures is known to a person skilled in
the art as monomorph- or bimorph-deflectable cantilevers or
membranes (beams or plates). The lateral force F (more accurately:
lateral strain caused by the physical effect) can be caused by
different physical effects: Thermomechanical excitation
(thermomechanical bimorph): Here, two materials 201 and 202 having
different coefficients of linear expansion are firmly connected to
one another. When this structure is heated (for example by an
integrated electrothermal micro heating=usage of the resistive
power), a lateral strain results and hence a lateral force of
different intensities in both layers. Due to this, the
microstructure is bent. Piezoelectric and electrostrictive
excitation (electroactive monomorphs, bimorphs and multimorphs
using the transversal effect): Here, a lateral strain or force is
generated within at least one layer 201 by an electrostatic field
and by using an electroactive material. This material strain can be
actively changed using the electric voltage or the electric field.
As a result of this, the microstructure is bent. Piezomagnetic and
magnetostrictive excitation (magnetoactive monomorphs, bimorphs and
multimorphs using the transversal effect): Here, a magnetic field
and the usage of a magnetoactive material generate a lateral strain
within at least one layer 201. As a result, the microstructure is
bent.
For appropriate ratios of maximum deflection w to beam or plate
thickness t (w<t), a spherical deformation profile results. This
results in the fact that the maximum deflection w is proportional
to the square of the length l of the microstructures
(w.about.l.sup.2).
The advantage of the bimorph- or monomorph-deflectable
microstructures is that with relatively small actively adjustable
material strains large deflections result with sufficiently large
structure lengths l. The maximum possible deflections are not
limited (as in the above case) by the characteristics of the drive
principle.
A problem associated with thermomechanical excitation is that
basically sufficiently high material strains for bending
micromechanical cantilevers and plates can be generated by the
thermomechanical effect and a suitable material selection (for 201
and 202) [1], but the generation of the temperatures necessitated
for this is problematic for three different reasons: The height of
the temperatures that can be generated with a given power coupling
depends on the thermal insulation (more accurately, heat flow
balance) of the microstructures to be deflected with regard to
their environment. Depending on the size of the beam or plate area
to be heated, high thermal insulation of the structures to be
deflected might not be realized. Thus, a relatively high power
consumption of the microsystem is needed for generating the
temperatures necessitated for deflection. If a resistive micro
heating (=usage of ohmic "power loss") is used, the operating range
of the temperatures to be used for the target movement of the
cantilever or the plate will have to be above the maximum
environmental temperature of the target application. The reason for
this is that a resistive micro heating can only increase
temperatures. Thus, the microsystem has high power consumption even
at low target deflections [5]. Basically, the temperatures could be
both increased and reduced by using the Peltier effect, but due to
the low efficiency a microsystem having low power consumption is
not possible here either. The amount of heat capacity (e.g. of the
surrounding air) associated with the thermal insulation of the
microstructures to be deflected limits the maximum possible
velocity of the movement of the deflection. Due to the relatively
high heat capacities, the thermal cut-off frequency is in the
bottom Hz range [5], [16] even for the low dimensions of
microsystems. This has the following consequences: If bimorph beams
or plates having higher frequencies are to be moved in a
quasi-static manner, a significant reduction of the deflection has
to be accepted due to the low-pass behavior of temperature
generation. With step-like changes of the target deflection, the
microstructure to be deflected reacts in a very slow manner (due to
the low thermal cut-off frequency) and hence necessitates a lot of
time until the target deflection is reached.
Due to the above-stated limitations (large power consumption,
"constant preheating" and low cut-off frequency of deflection), the
thermomechanical effect is used very rarely for actively deflecting
plates or beams. A commercial microsystem using the
thermomechanical effect for actively deflecting microstructures is
not known on our part.
Problems accompanying excitation using electroactive or
magnetoactive materials are, for example, the following. In
microsystem technology, for example, primarily the usage of the
inverse piezoelectric effect is common (see also [4]). A problem,
however, is the usage of the common electroactive or magnetoactive
materials within semiconductor-compatible production plants
(frequently called "CMOS-compatible materials"): materials having a
high electromechanical or magnetomechanical material coupling (such
as the piezoelectric materials PZT, BaTiO.sub.3 or LiNbO.sub.3)
cannot be used in semiconductor-compatible production plants or
processes due to the possible contamination of the production
plants or processes. Basically, there are semiconductor-compatible
electroactive materials such as aluminum nitride or PVDF. However,
either the electromechanical material coupling is very low (such as
for aluminum nitride or gallium nitride) or these materials have no
temperature or long-term stable behavior (such as zinc oxide).
Optimizing the deposition conditions for high electroactive
material coupling is very expensive, and in some case the materials
have to be actively polarized afterwards. Magnetoactive materials
basically have the problem of high power consumption of the
microcomponent (similar to the thermomechanical principle), since a
magnetic field having an alterable field strength has to be
generated for actively deflecting the material. Generating a
variable magnetic field can only be performed by a variable current
flow of a coil assembly having sufficient current strength. Usage
of permanent magnets is not possible here, since the same generate
a "stationary magnetic field".
In summary, it would therefore be desirable to have an alternative
drive principle for a micromechanical device uniting at least some
of the advantages of the different drive principles briefly
sketched above, and without having to accept all the accompanying
disadvantages.
SUMMARY
According to an embodiment, a micromechanical device may have: an
electrode; a deformable element; and an insulating spacer layer,
wherein the electrode is fixed to the deformable element via the
insulating spacer layer, and wherein the insulating spacer layer is
structured into several spaced-apart segments along a lateral
direction, so that by applying an electric voltage between the
electrode and the deformable element an area force acting in a
thickness direction is applied to the electrode and the deformable
element, as a consequence of which lateral tensile or compressive
forces result that bend the deformable element along the lateral
direction according to the bimorph principle.
Another embodiment may have a sensor having an inventive
micromechanical device, further having a detector circuit for
detecting the capacitance between the electrode and the deformable
element of the micromechanical device.
Another embodiment may have an energy generator comprising an
inventive micromechanical device, further having a voltage source
for applying a constant voltage between the electrode and the
deformable element, so that due to an externally induced bending of
the deformable element a current flow is generated between the
electrode and the deformable element.
The basic principle underlying the present invention is the finding
that it is possible to combine the different advantages of the
different known drive principles so as to reach a more effective
drive mechanism. In particular, the finding is that it is basically
very profitable to use the bimorph or monomorph principle for
deflecting beams or plates or other deflectable structures or
deformable elements since a small lateral material strain can
result in a large deflection due to the context already presented
above, according to which the deflection w is proportional to the
square of the length of the structure to be deflected or the
deformable element, i.e. w.about.1.sup.2. The inventors have
recognized that it is possible to generate the necessitated
material strain or contraction without the thermomechanical,
electroactive or magnetoactive effects involving the problems
discussed in the introductory part of the description. In
particular, it is a finding of the present invention that it is
possible to effect deformation of a deformable element according to
the bimorph or monomorph principle by electrostatic forces. Since
the forces on the electrodes of an electrostatic field in the plate
capacitor assembly scale very well in the micrometer and even
considerably more so in the nanometer range, due to the correlation
F.about.1/d.sup.2, it is extremely advantageous to generate lateral
strain or mechanical stress on or within a deformable element or a
structure to be deflected using electrostatic forces. Thus, the
present invention is also based on the finding that it is possible
to use the force on the electrodes of an electrostatic field such
that lateral tensile or compressive forces result which can deform
a deformable element or deflect a deflectable structure. According
to the invention, this is enabled by the fact that a
micromechanical device comprises, apart from an electrode and a
deformable element, an insulating spacing layer, via which the
electrode is fixed to the deformable element, wherein the
insulating spacer layer is structured into several spaced-apart
segments along a lateral direction, such that by applying an
electric voltage between the electrode and the deformable element
lateral tensile or compressive forces result that bend the
deformable element along the lateral direction. Due to the
inventive structure, the problem normally occurring with
electrostatic drives, namely the problem of the pull-in effect, is
overcome. Thus, according to the invention, deflection of the
deformable element can be much larger than the gaps of the two
electrodes, i.e. the above-mentioned electrode and the deformable
element.
Alternatively or additionally, it is also possible, in the
above-mentioned manner, to use a micromechanical device having an
electrode, a deformable element and an insulating spacer layer via
which the electrode is fixed to the deformable element as a sensor
by structuring the insulating spacer layer along a lateral
direction into several spaced-apart segments such that a
capacitance between the electrode and the deformable element
changes by deformation of the deformable element in the lateral
direction.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will be detailed subsequently
referring to the appended drawings, in which:
FIG. 1 is a schematic cross-section of a plate capacitor assembly
indicating the acting forces for positive lateral contraction;
FIGS. 2a to 2c is a schematic cross-section of different plate
capacitor assemblies having tilted electrodes indicating the acting
forces for positive lateral contraction;
FIGS. 3a and 3b is a schematic cross-section of further plate
capacitor assemblies having tilted electrodes indicating the acting
forces for positive lateral contraction;
FIGS. 4a and 4b is a schematic cross-section of "plate" capacitor
assemblies having tilted electrodes indicating the acting forces
for negative lateral contraction;
FIG. 4c are schematic force diagrams for illustrating the
occurrence of negative lateral contraction;
FIG. 5 is a schematic cross-section of a "plate" capacitor assembly
having tilted electrodes indicating the acting forces for negative
lateral contraction;
FIG. 6a is a schematic cross-section of a micromechanical device in
the form of an electrostatically bimorph-deflectable and one-side
clamped cantilever;
FIG. 6b is a schematic top view of the cross-sectional view of FIG.
6a;
FIG. 7 is a block diagram of a simplified functional chain of the
physical quantities acting in the micromechanical device of FIGS.
6a and 6b;
FIG. 8 is a schematic cross-section of a micromechanical device in
the form of an electrostatically bimorph-deflectable and one-side
clamped cantilever according to a further embodiment;
FIG. 9 is a schematic cross-section of a micromechanical device in
the form of an electrostatically bimorph-deflectable and one-side
clamped cantilever according to a further embodiment;
FIG. 10 is a dimensioned drawing of a micromechanical device in the
form of a cantilever, for which a simulation has been
performed;
FIG. 11 is a graph showing the z deflection of the beam of FIG. 10
in dependence on the location x at U=50 V;
FIG. 12 is a graph showing the maximum deflection of the beam at
the beam end of FIG. 10 in dependence on the applied electric
voltage U;
FIG. 13 is a graph showing the "equivalent layer stress" of a 200
nm thick layer in dependence on the applied electric voltage U at
electrodes of the cantilever of FIG. 10, which would result in a
comparable deflection w.sub.max of the beam.
FIGS. 14a to 14g are simplified schematic cross-sections of a
micromechanical device in subsequent stages of the production of
the same according to an embodiment;
FIG. 14h is a top view of the final state of FIG. 14g;
FIG. 15 is a schematic cross-section of a micromechanical device in
the form of an electrostatic bimorph-deflectable and one-side
clamped cantilever according to a further embodiment;
FIG. 16 is a schematic cross-section of a micromechanical device in
the form of an electrostatic bimorph-deflectable and one-side
clamped cantilever according to a further embodiment;
FIG. 17 is a schematic cross-section of a micromechanical device in
the form of an electrostatic bimorph-deflectable and one-side
clamped cantilever according to a further embodiment;
FIG. 18 is a schematic three-dimensional view of a micromechanical
device in the form of an electrostatic bimorph-deflectable and
one-side clamped cantilever according to a further embodiment;
FIG. 19 is a schematic cross-section of a micromechanical device in
the form of an electrostatic bimorph-deflectable and one-side
clamped cantilever according to a further embodiment;
FIG. 20 is a schematic cross-section of a micromechanical device in
the form of an electrostatic bimorph-deflectable and one-side
clamped cantilever according to a further embodiment;
FIGS. 21a to 21c are schematic cross-sections of a micromechanical
device in the form of an electrostatically bimorph-deflectable and
one-side clamped cantilever according to a further embodiment;
FIG. 22a is a schematic cross-section of a micromechanical device,
here exemplarily in the form of an electrostatically
bimorph-deflectable and one-side clamped cantilever for deflection
within a plane according to an embodiment;
FIG. 22b is a schematic top view of the side view of FIG. 22a;
FIGS. 23a to 23d are simplified schematic top views of a
micromechanical device at different stages of the production of the
same according to an embodiment;
FIG. 23e is a schematic side sectional view of the top view of FIG.
23d;
FIGS. 24a to 24d are simplified schematic top views of a
micromechanical device at different stages of the production of the
same according to an embodiment;
FIG. 24e is a schematic top view of an electrostatically
bimorph-deflectable and one-side clamped annular cantilever for
deflection within a plane;
FIG. 25a is a top view of a micromechanical device according to a
further embodiment in the form of a circular mirror plate connected
to a stationary frame by four spring elements, with the option of
actively bending the mirror plate, for example to obtain active
focus variation;
FIG. 25b is a side sectional view along the sectional plane A-A of
FIG. 25a in the non-deflected state of the mirror plate;
FIG. 25c is a side sectional view along the sectional plane A-A of
FIG. 25a in the deflected state of the mirror plate;
FIG. 26a is a schematic top view of a micromechanical device in the
form of a rectangular mirror plate connected to a stationary frame
by two beam-shaped spring elements which are also actively
bendable, according to an embodiment;
FIG. 26b is a schematic side sectional view along the sectional
plane A-A of FIG. 26a in the non-deflected state;
FIG. 26c is a schematic side sectional view along the sectional
plane A-A of FIG. 26a in the deflected state;
FIG. 27 is a schematic diagram for generating a torque using a
parallel beam structure with bendable beams according to an
embodiment;
FIG. 28 is a schematic top view of a micromechanical device in the
form of a circular mirror plate connected to a stationary frame by
two Y-shaped spring elements which are themselves actively
bendable, according to an embodiment;
FIG. 29 is a schematic top view of a micromechanical device in the
form of a circular mirror plate connected to a stationary frame by
two Y-shaped spring elements which are themselves actively
bendable, according to a further embodiment;
FIG. 30 is a schematic top view of a micromechanical device in the
form of a circular mirror plate connected to a stationary frame by
two Y-shaped spring elements which are themselves actively
bendable, according to a further embodiment;
FIG. 31 is a schematic top view of a micromechanical device in the
form of a circular mirror plate connected to a stationary frame by
two Y-shaped spring elements which are themselves actively
bendable, according to a further embodiment;
FIG. 32 is a schematic top view of a micromechanical device in the
form of a circular mirror plate connected to a stationary frame by
two Y-shaped spring elements which are themselves actively
bendable, according to a further embodiment;
FIG. 33 is a schematic top view of a micromechanical device in the
form of a circular mirror plate connected to a stationary frame by
two Y-shaped spring elements which are themselves actively
bendable, according to a further embodiment;
FIG. 34 is a schematic top view of a micromechanical device in the
form of a circular mirror plate connected to a stationary frame by
two Y-shaped spring elements which are themselves actively
bendable, according to a further embodiment;
FIG. 35 is a schematic top view of a micromechanical device in the
form of a circular mirror plate connected to a stationary frame by
two Y-shaped spring elements which are themselves actively
bendable, according to a further embodiment;
FIG. 36a is a schematic top view of a micromechanical device in the
form of a rectangular mirror plate connected to a stationary frame
via .quadrature.-shaped springs, which are themselves provided with
actively bendable portions, according to an embodiment for tilting
and translation of the mirror plate;
FIG. 36b is a schematic side sectional view along the sectional
plane A-A of FIG. 36a;
FIG. 37 is a schematic top view of a micromechanical device in the
form of a rectangular mirror plate connected to a stationary frame
via .quadrature.-shaped springs, which are themselves provided with
actively bendable portions, according to a further embodiment for
tilting the mirror plate;
FIG. 38 is a schematic top view of a micromechanical device in the
form of a rectangular mirror plate connected to a stationary frame
via .quadrature.-shaped springs, which are themselves provided with
actively bendable portions, according to a further embodiment for
tilting and translation of the mirror plate;
FIG. 39 is a schematic top view of a micromechanical device in the
form of a rectangular mirror plate connected to a stationary frame
via .quadrature.-shaped springs, which are themselves provided with
actively bendable portions, according to a further embodiment for
tilting and translation of the mirror plate;
FIG. 40 is a schematic top view of a micromechanical device
according to an embodiment in the form of a gimbally suspended 2D
tilted mirror assembly, where the inner mirror plate is connected
to a stationary frame via a movable frame, and the inner mirror
plate is able to perform a tilting movement around an axis and the
movable frame a tilting movement around an axis arranged
rectangular thereto;
FIG. 41 is a schematic top view of a micromechanical device
according to an embodiment in the form of an actively bendable
mirror plate with 2D tiltability;
FIG. 42 is a schematic cross-sectional view of a micromechanical
device according to an embodiment in the form of an AFM cantilever
for AFM with dynamic excitation or a non-contact mode or an
intermitting mode;
FIG. 43 is a schematic cross-sectional view of a cantilevered beam
or a plate deflected by a vertically effective force;
FIG. 44 is a schematic cross-sectional view of a cantilevered beam
or a plate deflected by the force of an electrostatic field;
FIG. 45 is a graph showing the basic curve of the normalized
deflection of a beam or a plate according to FIG. 44 in dependence
on the normalized electric voltage; and
FIG. 46 is a schematic cross-sectional view of a cantilevered beam
or a plate deflected by a lateral strain in at least one layer.
DETAILED DESCRIPTION OF THE INVENTION
Before embodiments of the present invention will be discussed in
more detail below, at first, the basic principle or the basic
effect underlying the subsequently described embodiments will be
discussed or justified in more detail. At first, geometries for
positive lateral contraction will be presented.
FIG. 1 shows the cross-section of a simple plate capacitor assembly
300. Here, electrodes 301 and 302 are arranged spaced apart from
each other at a distance d using an electrically insulating
material 303. The gap 304 between the electrodes can be filled with
air, another gas or can be evacuated (vacuum) and has the
permittivity .di-elect cons.. If an electric voltage U is applied
over the electrodes 301 and 302, an electrostatic field E will be
formed. The electrostatic field exerts a vertical force F.sub.z on
both electrode areas.
If the electrodes 301 and 302 are effected in a very stiff manner
(e.g. by materials having a high elasticity module or by a
sufficient thickness), i.e. they carry out only a very small
movement, the area force Fz/A acts on the electrodes:
##EQU00001##
This area force can assume very high values. If, for example, the
electrode plates are spaced apart from one another at a distance
d=100 nm, and there is air between the plates (.di-elect
cons.=8.8510-12 AsV.sup.-1m.sup.-1), then, at an electric voltage
of 10 V, an area force of 44 kN/m.sup.2 is exerted on both
electrodes. Producing plate gaps in the range of hundreds of
nanometers is possible in a relatively simple manner with the
sacrificial layer technologies known in microsystem technology.
As a consequence of the vertically acting forces of the
electrostatic field Fz, the horizontally acting reaction forces Fx
result (FIG. 1). This effect is to be understood analogously to the
effect of lateral contraction known in structural mechanics. The
effect can be significantly increased by slightly tilting one or
both electrodes. In the exemplary assemblies in FIGS. 2a-2c, the
top electrode 301 or both electrodes 301 and 302 have been tilted
by an angle .alpha.. The examples 300, 400, 500 and 600 can be
compared to the effect of a positive lateral contraction.
Even for small tilting angles .alpha., as are shown in FIGS. 3a,
3b, horizontal forces Fx pointing away from each other result from
the vertical force of the electrostatic field Fz. For angles
.alpha.<45.degree., this "force conversion" can also be
compared, to the effect of positive lateral contraction known from
structural mechanics.
The above preliminary consideration can be continued for
"geometries for negative lateral contraction". If the angle .alpha.
is increased to more than 45.degree. in geometries 700 and 800 (the
plate capacitors of FIGS. 3a, 3b), then the vertical forces Fz will
generate horizontal force components Fx pointing towards each
other. This principle can be compared to the effect known as
negative lateral contraction in structural mechanics.
For understanding "negative lateral contraction", planar rigid
supporting structures (=bar structures wherein the bars are ideally
rigid and cannot be deformed) can also be used. In the left-hand
images of FIG. 4c, the vertical force Fz is converted into reaction
force components Fx acting towards the outside, corresponding to
positive lateral contraction. In the right-hand drawing of FIG. 4c,
by the setting angle of the top electrode (.alpha.>45.degree.,
see FIGS. 4a to 5), reaction forces Fx pointing towards each other
are generated, which is referred to as "negative lateral
contraction". This could be shown based on the equilibrium of
forces (or force and momentum equivalence), which is, however, not
easily possible in this specific case, since this is an
under-determined equation system. The proof of the negative lateral
contraction has been performed by means of FEM calculations.
However, the large angle .alpha. is unfavorable for two reasons:
geometries 900 and 1000, as shown in FIGS. 4a, 4b, can only be
produced very poorly using sacrificial layer technology, and higher
drive voltages are necessitated due to electrode gaps that are on
average larger. A remedy is provided by the geometry shown in FIG.
5. This geometry again can be generated on a pre-structured
substrate using the sacrificial layer technology.
The above-discussed plate capacitors are provided on or within a
deformable element, such as a cantilevered beam or a cantilevered
plate, according to embodiments discussed below, to obtain the
desired deformation by the resulting lateral forces.
With the above-discussed plate capacitor geometries, it has been
shown how the forces F.sub.z resulting from the electrostatic field
can be converted to horizontally acting forces F.sub.x. The main
idea of subsequent embodiments for actuators is the usage of the
horizontally acting forces to be able to actively bend beams and
plates. For this, the plate capacitors are mounted on or within a
cantilever or a deformable element.
FIGS. 6a, 6b show a cantilevered beam as an example of a deformable
element (top view 1200 and cross-section 1300). Here, an insulating
material 303 and an electrically conductive material 301 are
deposited above an electrically conductive beam 1201. The
insulating material 303 can be laterally structured, for example by
a sacrificial layer technology, so that a thin cavity 304 is formed
between the electrodes 1201 and 301. The cavity has the thickness
of the dielectric sacrificial layer and thus defines the plate gap
of the capacitor. If an electric voltage is applied between the
electrodes 1201 and 301, a lateral strain on the surface of the
beam will result from the vertical forces of the electrostatic
field. As a consequence of the surface strain, the beam will be
deflected (in analogy to the above-described bimorph or monomorph
principle). If, as is shown in 6a, 6b, regular lateral geometries
are used, the surface strain will be approximately constant and a
spherical deformation profile w(x) results.
In other words, FIGS. 6a and 6b show a micromechanical device
having an electrode 301 and a deformable element 1201 exemplarily
implemented as a cantilevered beam or plate in the present case,
which could, however, also be implemented differently, as is also
the subject matter of the figures described below, and an
insulating spacer layer 303, wherein the electrode 301 is fixed to
the deformable element 1201 via the insulating spacer layer 303,
and wherein the insulating spacer layer 303 is structured in
several spaced-apart segments along a lateral direction 305
coinciding with the x direction in FIGS. 6a and 6b, which are
illustrated in a shaded manner in FIGS. 6a and 6b, so that by
applying an electric voltage between the electrode 301 and the
deformable element 1201, lateral tensile or compressive forces
result that bend the deformable element along the lateral direction
305, here the positive or negative z direction. Here, as shown in
FIG. 6b, the segments can each comprise a longitudinally extending
direction running transversally to the lateral direction 305. In
the embodiment of FIGS. 6a and 6b, the segments are implemented in
a stripe-shaped manner. The same obviously also applies to the gaps
304 between the same.
The deformable element 1201 does not necessarily have to be a plate
or a beam. An implementation has a bowl, membrane or bar is also
possible. In particular, the deformable element 1201, as in the
case of FIGS. 6a and 6b, can be suspended and clamped such that the
same remains unbent by applying the electric voltage U along a
lateral direction, here the y direction, perpendicular to the
lateral direction 205. However, the following embodiments will also
show that the deformable element can be suspended and clamped such
that the same bends in the same direction as along the lateral
direction 305 when the electric voltage U is applied between the
electrode and the deformable element along the lateral direction
perpendicular to the lateral direction 305. The result is a bowl-
or helmet-shaped bending, in which, for example, the direction 305
corresponds to the radial direction and the above-mentioned common
direction of the bending points along the thickness of the
insulating layer 303 from the electrode 301 to the deformable
element 1201.
As is indicated by the coordinate system in FIGS. 6a and 6b, the
micromechanical device can be formed in a substrate, such as a
wafer or a chip, such that the electrode 301 is fixed above or
below the deformable element 1201 in a substrate thickness
direction, i.e. the z direction, so that by the bending of the
deformable element 1201 the same is bent out of a substrate plane
corresponding, for example, to the resting position of the
deformable element 1201, namely in the bending direction pointing
in the opposite direction of z in the case of FIGS. 6a and 6b.
However, subsequently alternative embodiments will be described,
according to which the micromechanical device can also be formed in
a substrate such that the electrode 301 is laterally fixed to the
deformable element, so that by bending the deformable element the
same is bent within the existing substrate plane.
The height of the deflection of the beam or the plate or the
deformable element 1201 can be actively varied by changing the
electric voltage. The underlying physical principle can also be
explained by the functional chain (=conversion of the physical
quantities) in FIG. 7.
As is shown in FIG. 7, the electric voltage U generates an
electrostatic field which again has the effect that the electrode
301 and the deformable element 1201 are attracted towards each
other along the thickness direction or the z axis with the force
F.sub.z, wherein again the geometry and assembly of electrode 301,
deformable element 1201 and insulating layer 303 has the effect
that tensile or compressive forces F.sub.x are generated on or
within the deformable element or between the electrode 301 and the
deformable element 1201 which effect a bending w in the deformable
element. For a better understanding, it is assumed below that the
deformable element 1201 is a beam or a plate, wherein all these
specific embodiments can also easily be generalized.
As explained above, converting the vertical forces F.sub.z into
laterally acting forces F.sub.x can be significantly increased when
one or both electrodes are tapered (=tilted). The greater force
conversion is combined with a higher deflection of the beams or
plates. Accordingly, lower electric drive voltages are necessitated
for the same deflections.
FIG. 8 shows an embodiment where the top electrode 301 has been
tilted. This geometry can be generated, for example, by
pre-structuring the sacrificial layer for generating the cavity 304
already in its layer thickness before the electrode 301 is
deposited.
FIG. 8 shows that the electrode 301 can be formed in a planar
manner and between the segments of the insulating layer 303, in a
manner curved away from the deformable element 1201. In the
embodiment of FIG. 8, as was also the case in the preliminary
considerations with respect to FIGS. 1-5, the electrode 301 is
shaped such that the same has a V-shaped cross-section in a plane
between the segments of the insulating layer 303, which is spanned
by the lateral direction 305 and a thickness direction of the
insulating spacer layer 303, i.e. the xz plane. The curvature
could, however, also be implemented differently, in particular
without edges running laterally to the direction 305 or with a
differentiable curve along the direction 305. In the case of FIG.
8, the electrode 301 comprises, in each gap portion between the
segments of the insulating layer 303, two planar portions running
towards each other from immediately adjacent segments of the
insulating layer 303 and increasingly running away from the
deformable element 1201 to meet at an angle of
180.degree.-2*.alpha., wherein the definition of .alpha. of FIG. 2b
or 3a has been used, namely such that .alpha. states the angle of
these two planar portions with respect to the plane of the
insulating layer 303. Thus, for each gap 304, an edge in the
layer-shaped electrode 301 results, which runs in the center
between the segments of the insulating layer 303. The angle .alpha.
is, for example, between 1.degree. and 45.degree., each inclusive
of the same.
An embodiment where the surface of the bottom electrode or the beam
material 1201 has been pre-structured is shown in FIG. 9. FIG. 9
shows that also the surface of the deformable element 1201 facing
the electrode 301 can be formed in a curved manner between the
segments of the insulating layer 303, namely as shown in FIG. 9 for
example, facing the electrode 301. However, the surface could also
face away from the top electrode, as was the case in FIG. 2b.
Basically, all nine combination options are possible, according to
which the electrode 301 can be planar, curved towards the
deformable element 1201, curved towards the electrode 301 or away
from the same. Six of the options were shown in FIGS. 1a-3b. As is
also the case in FIG. 9, which corresponds to the example of FIG.
2c, the surface of the deformable element 1201 facing the electrode
301 between the segments of the insulating layer 303 can be formed
such that the same runs parallel to the layer-shaped electrode 301.
The insulating spacer layer can be planar. If the same has a bend,
it is smaller than the sectional bend or curvature of the electrode
301 and/or the respective surface of the deformable element
1201.
In order to be able to estimate the order of magnitude of the
above-described effects, the embodiment 1500 (in FIG. 9) has been
examined with the help of a finite element analysis. For this the
non-optimized geometry in FIG. 10 has been used: A cantilevered
beam of silicon having a length of 200 .mu.m and a thickness of
approx. 5 .mu.m represents the bottom electrode 1201. The surface
of the beam has been pre-structured such that an angle of slope
.alpha. of 5.degree. results. An insulating layer 303 of silicon
dioxide having a thickness of 100 nm is on the beam. The top
electrode 303 is 200 nm thick and also consists of silicon. The gap
between the electrodes is 100 nm. The individual electrode segments
have a length of 5 .mu.m.
For simplicity's sake, the following area loads independent of the
deflection of the electrodes have been applied between the boundary
layers: Boundary layer between 1201 and 304:
.times..times..times..times..times. ##EQU00002## Boundary layer
between 304 and 301:
.times..times..times..times..times. ##EQU00003##
With the help of the finite element model, the deflection of the
beam has been calculated. An exemplary deformation profile of the
whole beam at an electric voltage of 50 V is shown in FIG. 11 (x=0
is the suspension location).
The maximum deflection at the end of the beam in dependence on the
applied electric voltage is shown in FIG. 12.
If an approximately spherical deformation profile is taken as a
basis, an "equivalent layer voltage" .sigma. can be estimated from
the maximum deflection wmax of the beam, which needs to have a 200
nm-thick layer on a 5 .mu.m-thick beam so that the same experiences
a comparative bend:
.sigma..times..times..times. ##EQU00004## E.sub.beam and
.nu..sub.beam are the elasticity module and the lateral contraction
number of the beam, wherein the ratio of these elastic material
values is isotropic for (100)-oriented silicon:
.times..times. ##EQU00005## t.sub.beam corresponds to the thickness
of the beam (t.sub.beam.apprxeq.5 .mu.m), t.sub.film corresponds to
the thickness of the layer which will bend the beam due to the
mechanical (comparative) stress (t.sub.film=200 nm) and 1
corresponds to the length of the beam (l=200 .mu.m).
The equivalent layer stress calculated for the example in
dependence on the electric voltage is shown in FIG. 13: 1. The
characteristic curve illustrates that already at low electric
voltages high equivalent layer stresses (here compressive stress in
the MPa range) can be generated with the geometry of FIG. 10. Thus,
the effect is significant. 2. The curve of the exemplary
characteristic curve also shows that the usage of plate capacitors
for the bimorph or monomorph bending of plates or beams can be
compared to the usage of electrostrictive materials. With
electrostrictive materials, the actively generatable material
strain or material stress depends in a square manner to the
electric field or the electric voltage
(.fwdarw..sigma..about.U.sup.2). In other words, an
electrostrictive material can be substituted by the usage of plate
capacitor geometries shown in FIG. 10 on or within actively
deflectable cantilevers or other deformable elements. Since
standard materials can be used for producing the deflectable
structure or the deformable element, the above embodiments enable
the usage of an effect comparable to the electrostrictive effect
without having to use a material having high electrostrictive
material coupling.
In this computing example, the individual segments of the top
electrode 301 have been deflected in the z direction by less than
30 nm at an electric voltage of 50 V. Thus, the movement of the
electrodes has not yet reached the above-described unstable pull-in
region. At the same time (due to the force conversion of the
inventive structures) an overall deflection of the beam of more
than 2 .mu.m can be observed. Thus, the overall deflection is much
larger than the maximum movement of the electrodes and even
significantly higher than the gap of the electrodes.
Thus, the above as well as the following embodiments solve the
above-described "dilemma" of the pull-in effect, which so far has
occurred in conventional electrostatically deflectable
actuators.
Thus, the embodiments presented above allow the usage of
electrostatic fields for deflecting microstructures, wherein the
overall deflection can be significantly larger than the gaps of the
electrodes. This has not been possible so far. Thus, very small
electrode gaps and hence also low electric voltages can be used for
deflecting the microstructures. Thus, high drive efficiency is
enabled.
Thus, the above embodiments also have the advantage that
electrostatically deflectable microstructures have low power
consumption since electric current only flows at the time of
changing the electrostatic field, which is a great advantage
compared to thermomechanically, piezomagnetically or
magnetostrictively bimorph- or monomorph-deflectable beams or
plates.
The small electrode gaps between electrode 301 and deformable
element 1201 can be produced relatively easily by using the known
sacrificial layer technology. Semiconductor-compatible "standard
materials" can be used for producing the structures.
Actively bimorph- or monomorph-deflectable beams or plates can be
produced as a deformable element without using electroactive or
magnetoactive material. Thus, the problem of using materials having
high piezoelectric, electrostrictive, piezomagnetic or
magnetostrictive material couplings in solved, which may actually
not be used in semiconductor-compatible production processes.
The common piezoelectric materials, also having ferroelectric
characteristics (such as PZT or BaTiO3) have a hysteresis in the
characteristic curve of the material strain compared to the
electric field strength. If microstructures are deflected with
these materials, the characteristic curve of the device (deflection
in dependence on the control voltage) also has a hysteresis
function. Thus, the behavior of piezoelectrically deflectable
microstructures is not determined. On the assumption that the
mechanically strained components of the electrostatically, bimorph-
or monomorph-deflectable microstructures of the embodiments
presented and still to be presented are not plastically deformed,
such a microsystem has no hysteresis. An advantageous, determined
device behavior can be assumed.
A single disadvantage is that in plate capacitors having very small
electrode gaps, charge carriers can jump directly from one
electrode to the opposite electrode. This effect is known as "field
emission" and reduces the maximally usable electric voltage due to
the electric current flowing through the same. The strength of this
disadvantageous effect depends on the used electrode materials.
This disadvantageous effect can be limited in its extent by
selecting the electrode materials for the electrode 301 and the
deformable element 1201 in a suitable manner or by additionally
taking other measures, as they will be presented below, such as
providing thin insulating layers on the surfaces of the electrode
or the deformable element 1201 facing each other, or at least on
one of the same.
Before an exemplary production process for a micromechanical device
according to the above embodiments will be described below, it
should be noted that the deformable element 1201 can consist of a
conductive material, i.e. can be conductive itself, can be made
locally conductive, such as by doping, or can be coated with a
conductive material, such as with a metal coating, such as on the
side facing the electrode 301. The deformable element can consist
of a semiconductor material or another suitable material. The
insulating layer is also hardly limited with respect to the choice
of material. Advantageously, the same has a high rigidity and a
high electric resistance Like the deformable element, the electrode
301 can consist of a conductive material, can be made locally
conductive or can be coated with a conductive material.
As will be shown in the following discussion of an exemplary
production method, the deformable element might correspond to a
thinned region of a substrate, such as a semiconductor substrate,
wherein a merely local, e.g. one-sided or two-sided suspension,
optionally also in the form of respective spring elements, can be
realized in that an opening extending along a circumference of the
deformable element that is continuous in the thickness direction
separates respective portions of the circumference from the
otherwise rigid substrate. Alternatively, the deformable element
could, however, also have freedom of movement by being arranged
above a respectively large recession in the substrate, for example
by lateral etching.
An exemplary process flow for producing the inventive structures is
shown in FIG. 14. Here, the process is exemplarily started with a
BSOI (bonded silicon on insulator) wafer 1550 (step a), wherein the
SOI layer 1552 (top layer or device silicon) consists of silicon
with suitable doping for sufficiently high conductivity. Instead of
a BSOI wafer, obviously also another SOI wafer could be used. Even
variations with other types of wafer are easily possible. As is
shown, the wafer 1550 comprises a layer stack having a buried oxide
layer 1554 and a carrier substrate 1556 below the SOI or the
semiconductor substrate. As a first process step b) a silicon oxide
layer 1558 is applied, for example by means of deposition (with the
help of CVD deposition or thermal growth) whose thickness will
later define the electrode gap. In the following step c) a suitable
conductive material (e.g. an aluminum alloy, amorphous silicon or
amorphous titanium aluminide), which will later define the
electrode 301, is deposited, wherein the material is indicated by
1560. Subsequently, by suitable photolithographic process steps,
small holes 1562 are introduced into the topmost material layer
1560 (e.g. by reactive ion etching (RIE) for the later sacrificial
layer etching (step d)). The distance, the arrangement and the size
of the holes is selected, for example, such that the insulating
regions 303 remain due to the sacrificial layer etching (cf. step
B). Subsequently, a suitable rear-side lithography is performed on
the rear side of the BSOI wafer, so that in step e) the handling or
supporting silicon (=lowest layer or substrate of the BSOI wafer
1556) can be etched by wet chemical methods (TMAH or KOH etching),
but also possibly by deep reactive ion etching (DRIE) over a
suitable resist or hard mask. A large region 1564 results, defined
by the rear-side holes in a mask not shown in FIG. 14e having thin,
cantilevered membranes above the cavity 1564. In the subsequent
step f) etching of one or several open trenches 1566 is performed
for the edge of the cantilever (or another microstructure to be
deflected). The etching mask necessitated for this can, however,
also be applied prior to step e) and etching the SOI layer 1552 can
be performed by RIE, DRIE or possibly also purely chemically (e.g.
by XeF2 gas). In the release step g) sacrificial layer etching of
the uppermost SiO2 layer 1558 is performed. However, the buried
oxide layer 1554 is also etched, so that the trenches 1566 become
continuous openings. FIG. 14h shows a top view in which the
structure of the deformable element is shown more clearly as a
cantilever or a cantilevered beam or plate. Here, a suitable
etching solution flows through the etching holes 1562 introduced in
step d) and undermines or hollows out the top electrode layer 301
or 1562 to form the gaps 304. Theoretically, wet chemical methods
(e.g. with BOE) can be used for this, which is, however, not
advisable due to the strong surface forces of liquids and the
accompanying mechanical stress of the thin exposed structures
(so-called sticking effects can occur). As a good alternative, SiO2
sacrificial layer etching with the help of vaporous hydrogen
fluoride (vapor HF) is known and can be used for isotropic lateral
etching of the top electrodes 301. This vapor HF etching is to be
performed by a respectively selected etching period such that the
insulating material 303 or 1558 is maintained at a sufficient
width.
The "basic process" presented above and in FIG. 14 can be adapted
or improved by the following extensions or amendments: Instead of
the depositions b) and c), a multiple BSOI wafer (BSOI-SOI wafer)
can be used. Thus, the top electrode 301 also consists of silicon,
the layer necessitated for sacrificial layer etching is the top
SiO.sub.2 layer within the multiple BSOI wafer and the cantilever
or the microstructure to be deflected is realized by the central
silicon layer. The advantage of this approach is that the
mechanically stressed elements can be produced from single
crystalline silicon. Single crystalline silicon is well known (and
"popular") in microactuator engineering due to its excellent
mechanical rigidity. bent electrodes 301 but also the production of
the complex, e.g. sinusoidal electrode geometries (see FIGS. 15 and
16 below) can be realized by an appropriately produced
pre-structuring of the SOI layer 1560. For this, prior to step b)
the top silicon layer (SOI) is structured using wet or dry chemical
methods and structured via grayscale lithography or possibly
nanoimprint methods. Particularly the angle of 54.7.degree. shown
in the inventive examples (e.g. in 1100 in FIG. 5) can be generated
by TMAH etching in single crystalline, 100-oriented silicon.
Additionally, the top sacrificial layer 1558 can also be structured
by a suitable formative method prior to the deposition of the top
electrode 301 in step c) in order to produce further complex
electrode geometries. For example, a sinusoidal electrode geometry
can be enabled by merging silicon dioxide at a high temperature
which is above the glass transition temperature. For this, steps
are etched into the SiO.sub.2 layer, e.g. by a suitable dry etching
method. When heating these rectangular SiO.sub.2 steps above the
glass transition temperature, the material increasingly starts to
flow and strives to minimize its surface due to energetic
conditions. When the step distance and height as well as the
heating period are suitably selected, the energetically favorable
minimum surface corresponds to a sinusoidal curve.
The following embodiments 1600 to 2100 (in FIGS. 15 to 20) for
electrostatically deflectable beams cover only some, but not all
possible geometry variations, but serve for further illustration.
First, however, the following should be noted.
For example, as is shown in FIG. 15 and also pointed out above, it
is possible for the curvatures of the electrode 301 and/or the side
of the deformable element 1201 facing the same between the segments
of the insulating layer 303 to be less V-shaped but in fact
rounded. As is shown in FIG. 16, in the area portions of the
segments of the insulating layer 303 itself it is not necessitated
to implement the electrode 301 and the side of the deformable
element 1201 facing the same in a planar manner. Rather, the
corrugation of the electrode 301 and/or the side of the deformable
element 1201 facing the same can extend continuously across several
segments of the insulating layer 303 and its gaps 304. The
insulating layer 303 or its segments can, however, as is shown in
the embodiments, be formed in a common plane, i.e. in a planar
manner, so that for each curvature of the electrode 301 and/or the
side of the deformable element 1201 facing the same also an
oppositely designed curvature exists at the positions of the
segments of the insulating layer 303.
FIG. 17 shows, as has already been mentioned above, that
corresponding to the preliminary considerations in FIG. 2b, the
exemplary V-shaped curvatures of the electrode 301 in FIG. 17 and
the surface of the deformable structure 1201 facing away from the
same can be implemented pointing away from each other. FIGS. 18 and
19 show further options for micromechanical devices 1900 or 2000
corresponding to the implementations of FIG. 3a or 3b with respect
to the curvature of the top electrode 301 or the side of the
deformable structure 1201 facing the same. FIG. 20 shows another
micromechanical device 2100 where the portions between the segments
of the insulating layer 303 are formed according to the
implementation of FIG. 5, so that, by applying a voltage between
the electrode 301 and the deformable element 1201, deformation of
the deformable element 1201 in the direction of the z axis, i.e.
towards the top in FIG. 20, results, namely due to a lateral
contraction of the individual portions between the segments of the
insulating layer 303.
With respect to the above description, the following should be
pointed out. The previous embodiments all show that the periodic
portions exemplarily designated in FIG. 18 as three portions with
310a, 310b and 310c and extending between the immediately adjacent
segments of the insulating layer 303 were all structured equally,
i.e. with respect to the selection of the implementation of, for
example, one of FIGS. 1a-5, to the spacing of the segments in the
direction 305 up to the dimensions of the cross-sections of the
gaps 304. However, this is not necessarily so. Across the
individual portions 310a-310c, dimensions or implementations with
respect to the curvature of the electrode 301 or the surface of the
deformable element 1201 facing the same can also be varied. FIG. 18
is exemplarily shown as a three-dimensional drawing and it becomes
clear from this figure that the individual segments of the
insulating layer 303 are completely separate from one another and
also remain separate at the edge or lateral outer circumference of
the deformable element 1201, so that the gaps 304 are open at the
ends lateral to the direction 305 or at the ends opposing each
other laterally to the direction 305.
Additionally, it should be pointed out that in the above-described
embodiments the periodic plate capacitor assemblies were arranged
only on one of the main sides of the deformable element 301.
However, it is also possible for these periodically recurring plate
capacitor assemblies to be arranged on the top and the bottom of
the deformable element or above and below the neutral phase of the
deformable element. This is shown in FIG. 21a. If, as is shown in
FIG. 21a, an electrostatic actuator for generating lateral
compressive stress is mounted on the top and the bottom of the
deformable element 1201, i.e. the individual portions between the
segments of the insulating layer 303 correspond to the
implementations for positive lateral contraction, the deformable
element 1201 or the beam or the plate can be deflected in both
directions, i.e. in FIG. 21 towards the top or the bottom (or also
vibrating in a resonant manner) depending on how the electrode 301
is addressed. The same applies when the plate capacitors at the top
and the bottom are implemented for a lateral tensile stress or
correspond to the implementations for negative lateral
contraction.
In the case of FIG. 21a, the beam 1201 bends towards the top when a
voltage is applied between the top electrode 301 and the deformable
element 1201, and towards the bottom when this voltage is applied
between the bottom electrode 301 and the element 1201, while no
voltage is applied to the respectively different electrode pair.
However, it would also be possible for the plate capacitor
assemblies on the top of the deformable element 1201 to be
implemented for tensile stress or negative lateral contraction and
on the bottom for lateral compressive stress or positive lateral
contraction. In this case, deflection of the deformable element
could be amplified or the deflection could be increased with the
same electric drive voltage. In this case, a voltage would be
respectively applied both between the top electrode 301 and the
deformable element 1201 and between the deformable element 1201 and
the bottom electrode 301. The opposite configuration would, of
course, also be possible, according to which the capacitor
arrangements at the top are implemented for positive lateral
contract and at the bottom for negative lateral contraction.
Additionally, it would be possible to stack several planes of plate
capacitor arrangements or assemblies on top of each other so as to
result in a multiple actuator for increasing the curvature effect.
The options for this are shown in FIGS. 21b and 21c. Both figures
show that a further electrode 301 exists apart from the first
electrode 301, which is fixed to a side of the first electrode 301
facing away from the deformable element via a further insulating
spacer layer 303, wherein the further insulating spacer layer 303
is also structured into several spaced-apart segments along the
lateral direction. In FIG. 21b, the segments of the further
electrode 301 are positioned laterally in gaps of the segments of
the first electrode 301, while in the case of FIG. 21c the segments
of the two insulating layers 303 are oriented laterally to one
another, so that they oppose one another across the first electrode
301, as well as the respective gaps 304 between the same.
The implementation according to FIG. 21b, according to which the
actuator elements are each arranged offset by half a raster width
compared to the underlying actuator elements, reduces the
mechanical interaction of the actuator layers. In the
implementation according to FIGS. 21b and 21c, for bending, a
voltage is applied simultaneously both between the electrode 301 on
the one hand, and between the first electrode 301 and the
deformable element 1201 on the other hand, whereby the curvature
effect as described can be increased.
Previous embodiments were characterized in that a beam or a plate
can be bent out of the plane and hence be deflected in the z
direction due to the horizontal structure of the electrostatic
drives. This has been illustrated, among others, by the schematic
coordinate systems, wherein the x-y plane was parallel to the
substrate plane. The reason for this was the relatively simple
production of the small electrode gaps with the help of a thin
sacrificial layer.
However, basically it is also possible to build the structures in a
tilted manner, as is shown in FIG. 22. Here, the electrode areas
301 and 1201 are arranged orthogonally to the substrate plane. In
this way, microcomponents can also be deflected within the chip
plane (e.g. in the y direction in FIG. 22).
Thus, deflection of the deformable element 1201 in the plane of the
substrate in which the same is formed is possible with the
micromechanical device of FIG. 22. A possible production method
will be described below.
A bimorph or monomorph deflection of microstructures with in a
plane has so far only been possible using thermal excitation (e.g.
[19] or with the hot arm principle: [29]). As far as is known, the
electro- or magnetoactive effects cannot be used here, since it is
difficult to deposit respective materials having the necessitated
layer characteristics, e.g. on the side wall of beams. Compared to
thermomechanical excitation, the electrostatically monomorph- or
bimorph-deflectable actuators have low power consumption. Thus,
energy-efficient monomorph or bimorph deflection of microstructures
can be enabled within the chip plane. This has not been possible so
far.
In the following, an exemplary production process will be described
for the embodiment of FIG. 22 with deflection within a chip
plane.
Although producing these structures is not as easy as for FIGS.
1-21c, it is not impossible using technologies common for
microsystems. In particular by the increasing minimization of the
minimum structure widths in microelectronics, it can be expected
that the lateral structure widths in the range of 100 nm will
become usable also in microsystem technology. Currently, minimum
structure resolutions of approx. 1 .mu.m are common in microsystem
technology.
FIG. 23 shows an exemplary simplified process flow of the inventive
vertically structured structures. Here, small holes 1570 are
introduced into the device silicon 1552 of a suitable wafer (e.g.
BSOI wafer) using deep reactive ion etching (DRIE) (step b)). The
holes 1570 serve as segments of the insulating layer 303 or as the
locations of the same. In the subsequent step c), the small holes
1570 are filled with silicon oxide or another insulating material,
for example with the help of CVD deposition or thermal growth.
After that, by structuring with sufficiently high lateral structure
resolution, the gap 304 between the electrodes 301 and 1201 can be
etched using, for example, DRIE technology. In this step d), it is
also possible to simultaneously etch the contour 1574 of the
microstructures to be deflected (e.g. the edge of a beam) with
DRIE. The opening 1574 continuous in the substrate thickness
direction defines not only the contour of the deformable element
but also the deflectable path of the deformable element, which is
why the opening 1574 in FIG. 3d turns out to be more spacious. FIG.
23e shows the final state of FIG. 23d in a sectional view. As can
be seen, it can happen that the electrode and the deformable
element 1201 including the insulating spacer layer 303 in between
are formed only in the SOI layer 1552 of the wafer or the
substrate, wherein the buried oxide layer 1554 and the carrier
substrate 1556 can here be removed locally to release the movement
of the deformable element 1201. However, it can also be the case
that only the buried oxide layer 1554 is removed, whereas the
carrier substrate 1556 remains below the deformable element. After
all, it does not necessarily have to be an SOI wafer either.
As is illustrated in FIG. 24a, due to the lateral structuring (and
subsequent etching) it is possible to form any shapes of the gaps
304, but also any shapes of the top electrode 301. Thus, all
embodiments shown above with deflection in the z direction can be
produced. Additionally, the combinations shown in FIGS. 15-21c as
well as multiple layer actuators as well as combination of
actuators for generating lateral tensile or compressive strain are
possible above and below the neutral fiber and can be implemented
without any additional effort.
The process flow shown in FIG. 24 illustrates that it is suitable
for in-plane deflection of microstructures of any complexity. This
is illustrated in FIG. 24 on the basis of an annular beam. This
beam is firmly clamped at one end. If the electrostatic actuators
are mounted outside the neutral fiber (close to the edge) of the
beam, the radius of the annular beam changes due to a controllable
electric voltage. The free end of the beam performs a lateral
movement within the chip plane.
Any other shapes of a microstructure deflectable in this manner
are, however, also possible.
In the following, embodiments will be described where the above
embodiments are used in specific applications. Here, the structures
1200-2100 shown so far are used within actively deflectable
microdevices. The following section shows the usage of the
above-shown electrostatically deflectable beams and plates based on
several examples. These examples are, of course, not complete, but
are to illustrate the diversity of usage of the above-shown
micromechanical devices or variations thereof.
In the embodiment of FIG. 25, for example, a micromechanical device
similar to the one of the above-described embodiments is used to
result in an actively bendable micromirror for active focus
variation. A mirror plate having a round contour serves as the
deformable element, which is suitably suspended, wherein on a rear
of the same segments of an insulating spacer layer are formed in a
circular manner and concentrically to one another and to the
contour of the mirror plate, via which an electrode is fixed to the
rear of the mirror plate. Analogously to the above-described
embodiments, a lateral direction exists, namely the radial
direction along which the spacer layer is structured and along
which the mirror plate can be bent, depending on the implementation
of the plate capacitor portions for positive or negative lateral
contraction as a concave or collecting mirror or a convex
mirror.
FIG. 25 shows exemplarily an embodiment of an electrostatically
actively bendable micromirror for active focus variation. In this
figure, the thin black lines are open, etched trenches defining the
geometry of the solid body (between the lines). The circular mirror
plate 3001 is connected to a stationary frame 3003 via four elastic
spring elements 3002. On the bottom side 3004 of the mirror plate,
exemplarily the structure 1500 is mounted (see FIG. 25b). Applying
an electric voltage between the two electrodes 301 and 3001 of the
electrostatically deflectable structure effects a lateral
compressive strain on the bottom side 3004 of the plate. As a
consequence of the lateral compressive strain, the plate is bent in
a bowl shape, which is shown in FIG. 25c. If the lateral geometries
of the individual plate capacitor segments 310 are small compared
to the overall measure of the plate 3001 and additionally equally
distributed, an approximately homogenous radially acting surface
compressive strain on the bottom 3004 of the plate 3001 can be
assumed. Due to this homogenous surface strain, an approximately
spherical deformation of the plate 3004 is obtained.
If a reflection layer is deposited on the surface 3005 of the
plate, the structure 3000 can be used for active focus variation of
light. Here, changing the focal length of the concave mirror is
achieved by changing the electric voltage.
Possible extensions of the example of FIG. 25 are the
following:
When structures generating lateral tensile strain by the electric
voltage are used and are mounted on the bottom of the mirror plate
3001, the mirror plate experiences a helmet-shaped bend. The
helmet-shaped bend might possibly also be used for active focus
variation of light using a suitable optical system. All inventive
structures 1200 to 2100 can basically also be mounted on the top of
the mirror plate. However, it is a disadvantage that these
inventive structures (except 1200) have a surface topology due to
the bent electrode segments 301. Depending on the used wavelength
of the light to be focused, this surface topology can result in
mostly undesirable deflection and scattering effects in the
reflected light beam. Accordingly, if the structures are to be
arranged on the surface of bendable mirror plates, it can be
advantageous if a further planarization layer is deposited on the
top electrode 301 in the structures 1300 to 2100. This can be
performed, for example, by depositing a suitable thin layer and
planarization using the method of chemical-mechanical polishing
(CMP) known in microsystem technology. It is also possible to
generate local regions having compressive and tensile strain of
different heights on top or below the mirror plate using a
segmented arrangement of the structures 1200 to 2100 or by a
segmentation of at least one of the electrodes 301 or 1201 and
respective electric wiring. By this, the mirror plate is bent to
different extents at different locations. With this principle, a
micromirror is obtained for specific (not only purely defocusing)
influencing of the wavefront of light (so-called adaptive optical
mirror=AO mirror).
With reference to FIG. 26, an embodiment will be described below,
according to which a micro tilting mirror for spatially deflecting
light with the help of the above embodiments is obtained for a
micromechanical device. In this embodiment, the deformable element
forms a spring by which the mirror plate is suspended in a tiltable
manner. Bending the spring element or the deformable element leads
to the tilting.
The simple option for actively tilting plates using bimorph- or
monomorph-deflectable beam structures is shown in FIGS. 26a-26c.
Here, the (possibly rectangular) mirror plate 3101 is connected to
a stationary frame 3103 via one or several beam-shaped spring
elements 3102. Again, the forces of the electrostatic field of the
structures 1200 to 2100 are used (here exemplarily the structure
1500). For this, the structures are mounted on, within or on the
bottom of the beam-shaped spring elements 3102. The tensile or
compressive strain generated by the electric voltages again results
in an active bending of the spring elements 3102. As a consequence,
the plate 3101 mounted on the spring element is tilted, as is shown
in FIG. 26c. If this plate has a suitable mirroring layer on the
top side 3105 and/or the bottom side 3106, the same can be used for
spatially deviating light (e.g. one-dimensional light scan or beam
positioning within a plane). Deflection of the mirror can be
performed quasi-statically but also in a resonant oscillating
manner.
The option of an electrostatically bimorph- or monomorph-tiltable
mirror plate shown in FIG. 26 has the disadvantage that there is no
central rotation axis. This means that the rotation axis of the
tilting mirror does not coincide with a symmetry axis of the mirror
plate 3104. The subsequent implementations of micro tilting mirrors
for spatially deviating light have a central rotation axis.
It should further be noted that, as is shown in FIGS. 26b and 26c,
the spring element or the deformable element has a reduced
thickness compared to the mirror plate 3101, so that the mirror
plate 3101 is stiffer and hence more resistant against deformation
and, on the other hand, the spring element or the deformable
element can be more easily deformed. However, this is not
absolutely necessitated.
With the resonant drive, the voltage is applied between the
electrode 301 and the deformable element 1201 in the form of an
alternating voltage having a frequency that is defined in the range
of the mechanical resonance frequency of the spring-mass system
from the weight of the plate 3101, the spring and its restoring
force in the form of the deformable elements 1201.
A possible structure for generating the torque necessitated for
tilting (mirror) plates using monomorph- or bimorph-deflectable
parallel beam structures is shown in FIG. 27. Regarding the
principle, here reference is also made to [18]. Here, a structure
according to one of the above embodiments having actively
adjustable material strain is deposited on each control circuit
part 3152 and 3154 of the parallel beam structure 3150. If the
extent of the actively adjustable material strains of the active
layers of the beam is different (such as in FIG. 27, example 1,
shown by different signs of the strain), a torque 3158 is generated
at the joint 3156 of both beams.
In other words, FIG. 27 shows a parallel beam structure 3150 that
can be used for suspending tiltable plates, such as paraxial to a
mirror axis of the plate. The beam structure 3150 has two beams
3152 and 3154 arranged parallel to each other. At one end of these
beams 3152 and 3154 along their extension direction, the same are
connected to each other at a joint 3156, in order to be either
connected to the structure to be tilted not shown in FIG. 27 via a
common connecting beam 3160, or directly to the structure to be
tilted. At the opposite ends, the beams 3152 and 3154 are firmly
connected to the frame, which is also not shown in FIG. 27. On
their top 3162 or 3164 and/or their bottom 3166 or 3168, i.e. on
sides connecting the side areas of the beams 3152 and 3154 facing
each other and facing away from each other, the beams 3152 and 3154
are provided with one of the above structures of segments of the
insulating layer 303 and the electrode, so that one of the beams
3152 is bendable in the opposite z direction like the beam 3152 in
FIG. 27, and the other one in the opposite direction, i.e. the z
direction, in FIG. 27 the beam 3154, by applying a respective
voltage. By mutually bending the beams, the torque 3158 results,
and hence also a rotation of the suspended element, such as a
mirror plate.
With the parallel beam structures 3150 with structures 1200 to 2100
shown in FIG. 27, an actively deflectable tilting mirror as is
shown in FIG. 28 can be realized. In the electrostatically
deflectable tilting mirror of FIG. 28, the mirror plate 3201, which
is, for example, circular, is connected to the stationary frame
3203 via two Y-shaped flexible parallel beam structures 3202
(=Y-shaped spring elements) corresponding to the structure 3156 in
FIG. 27. Electrostatically, monomorph- or bimorph-deflectable plate
capacitor drives are above, within and/or on the bottom side of
each beam of the spring elements 3202. By changing the electric
voltage, the mirror plate can be tilted out of the plane, wherein
the tilting axis 3204 coincides with the central symmetry axis of
the mirror plate 3205, wherein the mirror plate 3201 is suspended
at opposite sides along this axis 3204 via the Y-shaped spring
elements 3202.
The example 3200 in FIG. 28 has two sub-actuator types generating
tensile or compressive stress. Additionally, further combinations
are possible: exchanging the inventive, electrostatically
deflectable cantilevers 1200 to 2100 is possible, which is shown in
FIG. 29. Additionally, it is also possible to use only one side of
the Y-shaped suspension of the mirror plate, which is shown in
FIGS. 30 and 31.
Additionally or alternatively, it is possible to provide the
structures for compressive or tensile strain generation on the
rear, i.e. on the side facing away from the mirror.
It can be useful to turn the Y-shaped suspension 3202 of the mirror
plate shown in FIGS. 28-31 by 180.degree., so that electrically
contacting the electrostatic actuators can be realized more easily.
In FIG. 32, this is shown exemplarily for all the combinations 3200
to 3500 discussed above. Here, the electric wiring of the top
electrodes 301 of the electrostatic drive can be realized by a
conductive trace 3601 which is routed to the stationary frame via
the beam structure. The second contact plane 1201 can be realized
by a respective conductive substrate for all actuators
together.
As was already shown with respect to FIG. 45, the maximum
deflection with support in monomorph- or bimorph-deflected plates
and beams is quadratically dependent on their structure length l.
Large deflections can only be obtained with long beams. In the
embodiments of electrostatically deflectable tilting mirrors
presented above, the lateral spatial requirement is disadvantageous
due to the necessitated lateral dimensions of parallel beam
structures 3202. A micro tilting mirror having a more compact drive
will be presented in the following section.
A possible embodiment for a micro tilting mirror for spatial
deflection of light, where the electrostatic actuator components
are placed on (in or below) sprint elements, which have an effect
in a distributed manner at the edge of an exemplary round mirror
plate, is shown in FIG. 33. This embodiment is known as
"distributed springs". Placing actuator components on the
distributed springs was already the subject matter of a patent
application and is explained extensively in patent application DE
102008049647. Here, again, the electrostatically actively
deflectable monomorph or bimorph beam structures 1200 to 2100 have
been used for deflecting the mirror plate.
In the embodiment of FIG. 33, here an exemplary circular mirror
plate 3201 is suspended via torsion springs running along the
tilting and mirror axis 3204, wherein, however, the torsion springs
3702 do not immediately have an effect at points along the
circumference of the mirror plate 3201, which lie on the tilting
axis, but at points 3703 distant from the axis 3204 along the
circumference. So-called distributed springs 3701, each implemented
in a beam shape and formed according to an actively bendable
structure according to one of the above embodiments of FIGS. 1-22,
lead from the torsion springs 3702 to these points 3703 along the
circumference. Simultaneously applying voltage to the structures
effects tilting of the mirror 3201 around the axis 3204, when
tensile strain generation structures are used on a lateral side and
compressive strain generation structures on the other lateral side
relative to the axis 3204 for the distributed springs 3701, as is
shown in FIG. 33. Thus, the distributed springs 3701 lead in a beam
shape along the circumference of the plate 3201 from the respective
torsion spring 3702 extending along the axis 3204 to the points
3703 distant from the axis along the circumference of the plate
3201.
Two further embodiments of a circular mirror plate, where the
electrostatic actuator components 3803 can be placed at at least
one of 12 possible locations in or below the distributed springs
3801 or 3901 according to the above embodiments, are shown in FIG.
34 and FIG. 35.
The embodiments of FIGS. 34 and 35 show clearly that already in the
embodiment of FIG. 33 the distributed springs do not have to
originate from a common torsion axis, but that each distributed
spring can have its own torsion axis. In the case of FIGS. 34 and
35, for example, the mirror plate 3201 is suspended
mirror-symmetrically to an axis 3805 which runs perpendicular to
the tilting axis 3204 and also represents a symmetry axis of the
mirror plate 3201 via eight distributed springs 3803 which have an
effect at eight different locations symmetrical to the tilting axis
3204 along the circumference of the mirror plate 3201 and extend
along the circumference of the mirror plate 3201 from the locations
of effect along the circumference of the mirror plate 3201 towards
the tilting axis 3204 to extend from there via the torsion springs
3802 to the suspension 3203, wherein a respective torsion spring
3802 running parallel to the tilting axis 3204 is allocated to each
distributed spring 3803. Thus, all in all, the eight distributed
springs 3082 have twelve portions which can comprise structures for
compressive strain or tensile strain generation according to one of
the structures 1200-2100, and, as has already been mentioned,
either on the front or the rear or both. The tilting principle in
the embodiments of FIGS. 34 and 35 is otherwise the same as in the
embodiments according to FIG. 33. For the distribution of possible
drive structures according to 1200-2100 of the above embodiments
onto the above-mentioned twelve possible portions of the
distributed springs 3803 offers in particular the following
combinations are advantageous: Actuators for tensile strain are
disposed above the torsion axis 3204 and actuators for compressive
strain are arranged only below the torsion axis 3204. As above,
only tensile and compressive strain exchanged or arrangement turned
by 180.degree.. Only actuators for tensile strain are arranged only
above or only below the torsion axis 3204. Only actuators for
compressive strain are arranged only above or only below the
torsion axis 3204.
In the following, examples of micro tilting and lifting mirrors are
described. In particular, an embodiment of a tilting mirror is
described which can be used simultaneously as a lowering mirror
having a translation movement in the z direction or substrate
thickness direction. Such a mirror is shown in FIG. 36.
Here, the exemplary rectangular mirror plate (3201) is mounted on
two .quadrature.-shaped spring elements 4001 and 4004. Up to 16
pieces of the inventive, electrostatically bimorph-deflectable
structures (1200 to 2100) are on, in or below the
.quadrature.-shaped spring elements. An actively adjustable lateral
strain in these structures has the effect of an S-shaped curvature
of the beams of the .quadrature.-shaped spring elements (see
section A-A in FIG. 36b), whereupon the edge of the mirror plate
experiences a deflection in the z direction. If a spring element
(e.g. 4004) is deflected, the mirror plate will be tilted around
its rotation axis 3204. An oscillating movement of this mirror
plate can also be effected by alternatingly deflecting both spring
elements 4001 and 4004. If both .quadrature.-shaped spring elements
are deflected simultaneously, the whole mirror plate is lifted. The
plate can hence be used as a lifting mirror.
In other words, the embodiment of FIG. 36 shows a mirror plate 3201
suspended at opposite sides along the circumference of the same,
via .quadrature.-shaped spring elements 4001 and 4004. Each
.quadrature.-shaped spring element 4001 and 4002 has two halves,
each comprising U-shaped spring portions facing each other with the
open side of the U. The two halves are connected to the mirror
plate 3201 and the suspension 3203 at the open ends of the Us.
Deflecting the mirror plate 3201 from its resting position at the
point at which a respective spring element is connected to the edge
of the mirror plate 3201 causes a curvature of the U-shaped halves
of the spring elements, as is illustrated in FIG. 36b. At each
U-shaped half 4005, four sequentially arranged portions result from
the connecting point 4006 along the edge of the plate 3201 to the
suspension location 3203, which alternately experience opposite
curvatures or curvatures in opposite directions, as can be seen in
FIG. 36b. Two of these four portions are at a leg 4007 of the
U-shaped halves 4005 and the other two at the other leg 4008 of the
U-shaped half 4005. As already mentioned above, the legs 4007 and
4008 are connected to one another in the closed section of the Us
via a connecting section 4009. Due to the opposite bends,
structures for generating opposite tensions, namely compressive and
tensile tensions provided with different reference numbers in FIG.
36, namely with the reference number 4002 for structures for
generating compressive strain and 4003 for structures for
generating tensile strain are arranged alternately along the four
portions. In this way, the mirror plate 3201 is suspended via a
total of four such U-shaped halves 4005, two of which respectively
form one of the spring elements 4001 and 4004.
Again in other words, FIG. 36 shows a rectangular mirror plate 3201
connected to a stationary frame 3203 via .quadrature.-shaped
springs 4001 and 4004, wherein in FIG. 36 again exemplarily the
bending structures are placed on the .quadrature.-shaped springs at
the above-mentioned 16 possible locations.
If the electrostatic drive elements 4002 and 4003 on one of the
.quadrature.-shaped spring elements are interchanged, the edge of
the mirror plate is moved in the negative z direction. This is
shown exemplarily in FIG. 37 for the spring element 4001. With this
arrangement, the mirror plate experiences tilting around the
rotating axis 3204 when the electrostatic drives of both spring
elements 4001 and 4004 are used or controlled simultaneously. The
tilting angle is approximately twice as large compared to the
arrangement in FIG. 26 with the same drive voltage of the
electrostatic drives. A lifting movement of the mirror plate is,
however, no longer possible with this arrangement.
The embodiments of micro tilting mirrors presented in FIGS. 36 and
37 can also be extended for spatial two-dimensional deviation of
light. For this, the assembly shown in FIG. 38 can be used. In this
example, the mirror plate 3201 has been connected to the stationary
frame via four .quadrature.-shaped spring elements (4001, 4004,
4201 and 4202). Depending on the deflection of the
.quadrature.-shaped individual spring elements, the mirror plate
can be tilted around both torsion axes 3204 and 4203. Simultaneous
tilting around both axes (for beam positioning within a plane) but
also a lifting movement (as a phase-shifting optical element) of
the mirror plate due to the simultaneous deflection of all
.quadrature.-shaped spring elements is also possible.
Analogously to the above-discussed exchange of electrostatic
actuator components, here almost doubling the titling angle is
possible. This is illustrated in FIG. 39.
As in FIGS. 36 and 37, the different reference numerals 4002 and
4003 in FIG. 38 are also to indicate the structures generating
different tensile or compressive stresses, namely reference numeral
4002 for structures generating compressive strain and reference
numeral 4003 for structures generating tensile strain.
Thus, FIGS. 38 and 309 each show a rectangular mirror plate 3201
connected to a stationary frame 4203 via four .quadrature.-shaped
springs 4001, 4004, 4201 and 4202, wherein here exemplarily
additionally to the .quadrature.-shaped springs the tensile or
compressive strain-generating structures 4002 and 4003 are placed
at the 32 locations possible here.
The last described embodiments for drive principles, base elements
and also production technologies or substrate can also be combined.
A possible combination is, for example, the arrangement of two
tiltable mirror plates gimbal-suspended to each other to allow
two-dimensional deviation of light. In the example of FIG. 40,
exemplarily, the basic structure 3700 was used here twice.
Basically, all tilting mirrors described above can be used, wherein
with the help of the gimbal suspension the same can be combined in
order to be used as a 2D tilting mirror.
A combination of a focusing mirror with a bendable mirror plate as
described with reference to FIG. 25 can also be combined with the
tilting mirrors described above or also with the arrangements 4000
or 4200 that can be used as lifting mirrors. An exemplary
combination assembly is shown in FIG. 41.
In particular, FIG. 40 shows a gimbal-suspended 2D tilting mirror
assembly wherein the inner mirror plate 3201 is connected to the
stationary frame 3203 via a movable frame 5003. The inner mirror
plate 3201 can effect a tilting movement around the axis 5002 and
the moving frame a tilting movement around the axis 5001. FIG. 41
shows a combination of an electrostatically actively bendable
mirror plate 3201 for beam focusing 3000 and the 2D tilting mirror
assembly 4200.
For atomic force microscopy (AFM), commonly thin beams (leaf
springs) having a measuring tip are used for material analysis
(surface roughness, domains having the same electric polarization).
For these measurement methods, measurement modes exist in which the
cantilever having the measuring tip is actively deflected or
operated in a resonant oscillating mode. Deflecting the beam can
also be performed by the above-described electrostatically
monomorph- or bimorph-deflectable cantilevers. FIG. 42 shows an
option for using the electrostatically deflectable cantilevers for
atomic force microscopy. In this example, exemplarily the structure
1500 is supplemented by the measuring tip 6001 necessitated for
AFM.
Finally, FIG. 42 shows an embodiment illustrating that the
above-described embodiments can also be used for atomic force
microscopy, namely as AFM cantilevers (cantilever=cantilevered
beam).
Thus, the above embodiments show, among other things, an
electrostatically deflectable micromechanical member wherein an
electrode 301 is arranged at a small distance 304 above a beam or a
plate 1201, in order to be able to actively bend the beam or the
plate 1201 by laterally acting tensile or compressive forces,
wherein the low electrode gap 304 is produced by an insulating
material layer 303. The electrodes of the electrostatic drive can
be laterally divided into several segments by laterally structuring
the insulating layer 303. Lateral structuring can be embodied
evenly, so that laterally acting and approximately constant tensile
or compressive strain results from the laterally acting tensile or
compressive forces. The electrode 301 and the insulating material
layer 303 can also be arranged within or below or above and below
the beam or plate 1201 to be actively bent. The electrode 301 can
be arranged in a tilted manner with respect to the plane, as was
the case in the embodiments for a device 1400 and 1900. The surface
of the beam or the plate 1201 can also be tapered by respective
structuring, wherein reference is made to the embodiments 1500,
1800, 2000 and 2100. The tilting angle is, for example, in a range
between 50.degree. and 60.degree. and is, for example, in
particular 54.7.degree..
The electrode 301 and/or the surface of the beam or the plate 1201
can also be implemented in a vertically wave-like shape, wherein
reference is made to embodiments 1600 and 1700. The wave-like
cross-section can be implemented to be sinusoidal, spherical or
oval. However, the cross-section can also correspond to any
function or can be described by any free form.
The electrode 301 and the insulating materials layer 303 can also
be arranged in several sheets stacked upon each other on, within
and/or below the beam or the plate 1201. In multiple actuators, the
individual segments can be arranged offset to each other by half a
structure.
Additionally, it is possible for the insulating material layer 303
to be also a sacrificial layer producing the gap of the electrode
301 by sacrificial layer etching. The gap between the electrode 301
and the beam or plate 1201 is, for example, between 100 nm and 5
.mu.m.
The beam or the plate 1201 or the electrode 301 can be produced of
a conductive material, for example a doped, single crystalline,
amorphous or polycrystalline silicon, germanium, silicon germanium,
silicon carbide or gallium arsenide. However, they can also consist
of aluminum or an aluminum alloy, such as AlMgSi, AlTiSi, AlSiCu,
of titanium, titanium aluminide or a titanium alloy.
The insulating layer 303 can again be formed of silicon oxide,
silicon nitride, aluminum oxide, aluminum nitride, titanium oxide
or titanium nitride.
On the surfaces of the electrodes 301 and 1201 facing each other,
an additional electrically insulating, i.e. the electric layer, can
be deposited to prevent or reduce the electric breakdowns caused by
the possible field emission effects or to prevent, at a possible
pull-in of the top electrode 301, the device from being
irreversibly damaged. Here, the dielectric layer can consist of
silicon oxide, silicon nitride, aluminum oxide, aluminum nitride,
titanium oxide or titanium nitride. The gap 304 between the
electrodes 301 and 1201 can be filled with a soft material, such as
a polymer, a liquid or any gas or vacuum.
The electrostatically bendable beam or the electrostatically
bendable plate can be used for deflecting microstructures, such as:
i. for tilting mirrors, lifting or lowering mirrors (=translation
mirrors), but also for tilting mirror and lowering mirror arrays,
ii. for focusing mirrors, but also for any deformable mirrors for
wavefront correction, iii. for active compensation of the bending
of mirror plates generated by intrinsic material tensions within
tilting, lifting or lowering mirrors (+arrays), iv. for actively
adjustable lenses or lens arrays, v. for dynamic excitation of leaf
springs within an atomic force microscope assembly, vi. for
variable electric capacities (MEMS Varicap or MEMS Varactor) or for
electric switches, vii. for usage within a micromirror array in an
active back plane (here: electro-optical circuit for addressing or
selecting individual information channels), viii. for acceleration
or rotational speed sensors. Generally, usage for micro positioning
is possible.
Using the structures as a sensor detecting a bending state or
deflection of a micro device by changing the electric capacitance
between electrodes 301 and 1201 is also possible, in addition or as
an alternative to the usage as an actuator.
However, the structure can also be used as a generator converting
motion energy into electric energy, i.e. for so-called energy
harvesting: for this purpose, a ground or a plate can be mounted on
the beam, which is deflected by external motion energy or by
airflow. Thereupon, the beam is bent, whereby the electrode gap 304
and hence the electric capacitance changes. At a deflected constant
electric voltage between electrodes 301 and 1201, a current flow
results due to the change of capacitance. Thereby, the electric
energy can be tapped or can be used for supplying autonomous
systems, for example.
However, the above structures can also be used for an actuator as
an integrated element for mounting microelements, such as optical
fibers, micromirrors and microlenses, mounted to the chip via
hinges and used for setting, adjusting or positioning the
microelements after singulation and mounting and connection
technology.
The usage of such actuators can also provide that the same are used
as cantilevered structures, without silicon chip or handling or
carrier substrate, such as within mechatronic applications, such as
for fine positioning.
The excitatory movement of the beam or plate can take place
quasi-statically or in a resonant manner.
Combining or integrating the microactuators with an electronic
circuit for their control can result in a respective system that
can fulfill respective functions.
As described above, for example with reference to FIGS. 22-24b, it
is also possible for the assembly to be structured in a vertical
manner, i.e. by placing the actuators above or below the neutral
fiber of the microstructure to be deflected. The usage of such a
lateral deflectable structure is, for example, for: i. an optical
aperture, such as an iris aperture, an optical shutter or an
aperture or shutter array, ii. a shutter array used within
transmissive displays, iii. the drive of a gear or a linear drive
(actuator).
A combination of the above microstructures would also be possible,
so that a microstructure, such as a beam, can be deflected in a
vertical direction, but also within a plane, wherein the usage of
such a structure could be intended for three-dimensional
positioning, such as as a micro gripper or for lateral positioning
and at the same time for a vertical deflection of a beam with a
measuring tip for atomic force microscopy, i.e. AFM with dynamic
excitation.
On the other hand, some of the above embodiments also showed an
electrostatically deflectable focusing mirror 3000, wherein an
electrode 301, which is deposited at a low gap 304 in an
electrically insulating manner by a laterally structured insulation
layer 303 is on, in or below the conductive mirror plate 3001, and
wherein the mirror plate is bent when an electric control voltage
is applied. Generally, the same variation options result as
described above in summary for the microdevice. The mirror plate
can experience an approximately spherical or parabolic bend, for
example to collect light at a central focal point. The mirror plate
can also have a rectangular, circular, elliptical or any, such as a
polygon-like, free form. The mirror plate can be connected to a
stationary frame 3003 at one or at several points at the plate edge
by suitable spring elements 3002. An additional planarization layer
can be provided for the case that the electrodes 301 and 1201 are
deposited on the front of the mirror plate and have a significant
topology, such as bent electrodes. Chemical-mechanical polishing
(CMP) can be used to level the deposited planarization layer. Such
a focusing mirror can be used to specifically correct or
arbitrarily deform or influence a beam profile. Thereby, electric
segmentation of at least one of the two electrodes 301 or 1201 can
be provided to be able to bend individual areas of the mirror plate
to a locally different extent by several electrically separate
control voltages. Such a device could be used as an adaptive
optical mirror for specifically influencing the phase front of
light waves.
Generally, such a focusing mirror 3000 can be used for
i. focusing laser beams when cutting, marking and welding
materials, ii. tracking the focus length in laser-based barcode
scanners, iii. zoom and focus applications in image-capturing and
imaging systems, such as projectors, photo cameras, confocal
microscopes and in optical coherence tomography and iv. reading out
multilayered optical data carriers, v. concave mirror arrays within
transmissive displays (in telescopic pixel displays).
Some of the above embodiments described electrostatically
deflectable tilting mirrors 3100 to 3900 wherein the mirror plate
3101 or 3201 is mounted on at least one beam 3102, 3202, 3701, 3801
or 3901, wherein an electrode 301 is on, in or below this beam,
which is mounted at a low distance 304 by a laterally structured
insulating layer 303 in an electrically insulating manner, and the
mirror plate is tilted when an electric control voltage is applied.
Again, the variation options can be applied which have been
described above with respect to the microdevice. The mirror plate
can have a rectangular, circular, elliptical or any, such as a
polygon-like, free form. The mirror plate 3201 can be connected to
the stationary frame 3203 via at least one Y-like parallel spring
structure 3202, as has been the case, for example, in the
embodiment 3200. Additionally, electrostatic drives can be placed
on, in or below the beams at two different positions on the Y-like
parallel spring structures, wherein reference is made to the
different assemblies 3200 to 3600. The mirror plate 3201 can also
be connected to the stationary frame 3203 by several distributed,
beam-like spring structures 3701, 3801 or 3901 and one or several
torsion springs 3702, 3802 and 3902 guided in parallel, wherein
reference is made to embodiments 3700, 3800 and 3900. The
electrostatic drives on, in or below the beam of the distributed
springs can be placed differently, wherein reference is made to the
different assemblies according to 3200 to 3600. Such
electrostatically deflectable tilting mirrors can, for example, be
used for i. data acquisition in 1D, 2D scanners and microscopy, ii.
data outputs in laser displays, laser printers, laser labeling or
exposing machines.
Some of the above embodiments also related to electrostatically
deflectable tilting, lowering and lifting mirrors 4000 to 4300,
where a mirror plate 3201 is mounted on at least one beam 4001,
4004, 4201 and 4202, wherein an electrode 301 is on, in or below
this beam, which is mounted at a low distance 304 in an
electrically insulating manner by a laterally structured insulating
layer 303, wherein the edge of the mirror plate is lifted or
lowered when an electric control voltage is applied. The variation
options that have been described above with respect to the
microdevice can also be applied here. As was described above, an
S-shaped curvature of the spring elements can be obtained by
suitably arranging the electrostatic drives, so that the edge of
the plate can be moved in one direction, such as the positive z
direction as in the case of the embodiment 4000, or in the negative
z direction as in the embodiment 4100. The usage of lifting or
lowering a plate edge can be used, for example, for tilting a
mirror plate, i.e. as a tilting mirror or for lifting or lowering
the mirror plate, such as, e.g., as a translation mirror.
The mirror plate can have a rectangular, circular, elliptical or
any, such as a polygon-like, free form. The usage of four spring
elements is also possible, as was shown in the embodiments 4200 and
4300. With this, a two-dimensional tilting movement can be
realized. The usage as a tilting mirror is, for example, possible
for i. data acquisition in 1D, 2D scanners and microscopy, ii. data
outputs in laser displays, laser printers, laser labeling or
exposing machines. The usage as a translation mirror is, for
example, possible i. in Fourier transform spectrometers,
interferometers, lamellar grating interferometers, ii. in confocal
microscopes or iii. in optical path length modulators.
Finally, an embodiment with electrostatically deflectable leaf
springs 6000 has been described, wherein one electrode 301 is
arranged at a small distance 304 above a beam 1201 in order to be
able to actively bend the beam 1201 by laterally acting tensile or
compressive forces, wherein the low electrode gap 304 is produced
by an insulating material layer 303 and a measuring tip is located
on the bottom of the beam. Here, the variation options which were
described above with respect to the microdevice can also be
applied. The beam can be cantilevered and connected to a stationary
frame. The usage of such a leaf spring can, for example, take place
in atomic force microscopes, such as for dynamic excitation.
It has been shown that the electrode 301 can be fixed in the
substrate thickness direction of the substrate 1550 in which the
micromechanical device can be formed, such as a BSOI wafer, above
or below the deformable element 1201, so that by bending the
deformable element 1201 the same is bent out of a substrate plane
along which the substrate extends, i.e. into the substrate
thickness direction. In this case, the spacer layer extends
parallel to the substrate plane, like the electrode 301 and the
deformable element 1201, when the same are formed in a planar
manner. Alternatively, the device can be formed in the substrate
(1550) such that the electrode 301 is fixed laterally to the
deformable element, so that by bending the deformable element the
same is bent within a substrate plane. In this case, the spacer
layer is then perpendicular to the substrate plane, just like the
electrode 301 and the deformable element 1201, when the latter are
formed in a planar manner.
A micromechanical device according to each of the above embodiments
can comprise, as is indicated by dotted lines in FIG. 6a, a driver
circuit 340 for applying the voltage U to the micromechanical
device, so that the micromechanical device acts as a
micromechanical actuator as was described above. In the case that
this is a micromechanical device of a sensor--such as an
acceleration sensor or the like--with an electrode 301, a
deformable element 1201 and an insulating spacer layer 303, wherein
the electrode is fixed to the deformable element 1201 via the
insulating spacer layer 303 and the insulating spacer layer 303 is
structured into several spaced-apart segments along a lateral
direction 305, so that by a deformation of the deformable element
1201 in the lateral direction a capacitance between electrode and
deformable element changes, the indicated circuit 340 in FIG. 6a
can be a detector circuit for detecting the capacitance between the
electrode 301 and the deformable element 1201 of the
micromechanical device. 340 could, however, also be a voltage
source for applying a constant voltage between the electrode 301
and the deformable element 1201, so that due to an externally
induced bending of the deformable element 1201a current flow is
generated between the electrode 301 and the deformable element 1201
and hence an energy generator is formed.
As was described above, the deformable element 1201 can form a
spring portion 3803 between a suspension location 3203 and a
functional element 3201 of the micromechanical device, wherein the
functional element can comprise a plate 3201 which is tiltably
suspended around a tilting axis, and the spring portion can form a
first distributed spring 3803 of the micromechanical device which
extends opposite to a second distributed spring of the
micromechanical device along a circumference of the plane from a
torsion spring 3802 extending along the tilting axis--namely a
respective one or a common one for the first and second distributed
spring--of the micromechanical device to a mounting location at the
circumference of the plate, namely symmetrical to the second
distributed spring. Here, a further electrode can be provided which
is fixed to the second distributed spring via a further spacer
layer, such that in the first distributed spring the insulating
spacer layer 303 is structured such that by applying an electric
voltage (U) between the electrode and the deformable element
lateral tensile or compressive forces result that bend the first
distributed spring relative to the plate in a first normal
direction, such as downwards or in the negative z direction, and
wherein in the second distributed spring the insulating spacer
layer 303 is structured such that by applying an electric voltage
(U) between the electrode the deformable element lateral tensile or
compressive forces result that bend the second distributed spring
relative to the plate in a second normal direction opposing the
first.
While this invention has been described in terms of several
advantageous embodiments, there are alterations, permutations, and
equivalents which fall within the scope of this invention. It
should also be noted that there are many alternative ways of
implementing the methods and compositions of the present invention.
It is therefore intended that the following appended claims be
interpreted as including all such alterations, permutations, and
equivalents as fall within the true spirit and scope of the present
invention.
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